The vertebrate life of a distant planet uses biogenic silica for structural support. However, biogenic silica is soluble in water, but (according to this article) its solubility decreases by having aluminum within its matrix. Thus, the idea is to have aluminum-based blood produced from within the biogenic silica bones.
What would the attributes of aluminum-based blood be?
I'm going to go for a slightly unsatisfactory answer here and say that you can make up anything you want and it'll be OK.
The problem is that there are no examples of biological processes that use aluminium. From the encyclopedia of metalloproteins, the entry for "aluminum in biological processes" says:
Aluminum is neither required by biological systems nor is it known to participate in any essential biological processes. While today all living organisms contain some aluminum, there is no scientific evidence that any organism uses aluminum for any biological purpose. There is similarly no evidence from the proteome or genome that any organism has utilized aluminum at any time in the evolutionary record. Aluminum’s abundance and paradoxical lack of biological function remains a biochemical enigma.
It is argued that aluminum’s absence from biochemical processes can be best explained in terms of its “historical” absence from biochemical evolution (Exley 2009a). In spite of its abundance in the Earth’s crust, aluminum was not biologically available for the greater part of biochemical evolution.
The linked reference (Using Darwin in helping to define the biological essentiality of silicon and aluminium) is behind a paywall, but does have some potentially interesting things to say...
aluminium’s slow ligand exchange rates are suggested to preclude any efficacy as a metal co-factor for enzymes
There is evidence in DNA that non-essential heavy metals such as cadmium have at a previous time in biochemical evolution been both encountered and selected out of biochemistry... There are no known designed-for-purpose mechanisms by which aluminium is specifically either kept out of or removed from biota, nor is there evidence in biochemical evolution of significant encounters between biota and biologically available aluminium. Therefore, even allowing for its ubiquity within the Earth’s crust, the logical explanation of the non-essentiality of aluminium must be that biochemical evolution has proceeded in the absence of biologically-reactive forms of the metal
This all adds up to say that there are no real-world examples of the chemicals you're interested in, and so no-one can really answer your questions in a useful way. Not only that, but the chances of aluminium-using biota arising naturally are pretty small in the first place.
I'd suggest that you stablise your silica parts with aluminium-bearing chemicals from the environment, but give up on the idea of aluminium-based blood.
If you weren't prepared to do that, then you could just handwave in any colors and flavors that you like, because no-one is realistically going to be able to prove you wrong.
Hemoglobin's transport of blood relies on its ability to reversibly bind its iron to oxygen. When hemoglobin releases oxygen, the iron captures water. When aluminum binds to ligands, it forms a strong bond and will not be able to easily release the captured oxygen. This makes it difficult for aluminum compounds to transport oxygen.
One alternative is a cell similar to a "respirocyte". Respirocytes are theoretical red blood cell substitutes with 236 times the capacity for oxygen storage. They are essentially nanoscale pressure vessels. A respirocyte would require a durable nanostructure. A nanostructure composed of aluminum nanograins encapsulated by aluminum-nickel metallic glass could allow your organisms to transport oxygen in aluminum cells or organelles. Some ribosome-like machine could synthesize these complex structures.
I don't know what color the blood would take on, but I do know that the color will not change between oxygenated and deoxygenated states because the oxygen is captured within a structure and not causing any chemical change. The ability to transport oxygen as I mentioned would be around 200 times greater than a red blood cell.
Information from The Ubiquity of Iron, Exploratory design in medical nanotechnology: a mechanical artificial red cell, Hierarchical nanostructured aluminum alloy with ultrahigh strength and large plasticity
Frame challenge
You don't need anything as exotic as aluminum to stabilize silicate bones. Silica is only weakly soluble in water, and you want it to be possible to redissolve to allow bone remodeling anyway. The solubility of silica is strongly dependent on pH, because SiO2 dissolves by attaching hydroxide groups to form silicic acid, Si(OH)4. Silica bones can thus be stabilized simply by embedding silica crystals in a protein matrix which protects them from attack by hydroxyl ions; or by simply making the blood slightly acidic; or both.
Aluminium is a tricky choice. It only forms soluble compounds at very low or very high pH. At high pH, you will not be able to deoxygenate it; you'll have a load of biologically useless aluminate ions.
Low pH is better; there are mixed species aluminium oxychlorides which can swap oxygen or chlorine in depending on pH, chlorine and oxygen concentration. The problem here is, they aren't soluble. The solution: nanoparticles.
Have the particles bonded to some organic bits that stabilise/control them, similar to an active metal site in a conventional enzyme (or the active cluster in photosystem II), in a blood teeming with HCl. When oxygen concentration is high, you replace chlorine with oxygen. The organic part of the enzyme does the work of regulating the details.
Your blood is white and milky regardless of oxygenation state. The lifeform is alien; we don't have blood with such low pH on earth.
Deodorant companies will try to slay your aliens by the billions and pack their blood into sticks / into emulsions on roller balls.
FWIW, I did my masters on certain synthetic amorphous aluminosilicates; I recommend keeping the bones separate from the blood question. Calcium phosphate is insoluble and we make bones out of it just fine (Our bodies take soluble calcium and phosphate separately and join them together as needed). If you want to stick Al in as a strengthening impurity, fine,but you won't easily make bones by precipitating aluminosilicates. If you really really want those bones and don't actually care about blood, google aluminosilicate geopolymers.
I'm not sure that you will like the answer, but aluminium salts are colourless. Aluminium is most commonly found in it's +3 oxidation state although +2 and +1 are known. Aluminium reacts very readily with oxygen forming its trivalent oxide Al2O3 which is very stable and also insoluble.
Biological aluminum can be reddish purple! However I don't know if this kind of molecule could carry oxygen the way an iron containing protein complex like hemoglobin can.
From Biology SE's Do cochineals ("scale bugs") form aluminum complexes themselves? Where do they get such large quantities so quickly and how do they handle it safely?
Click figures for full size. above first: "Figure 2. Salasaca dyer showing red woollen cloths with modified cochineal red colours. Ecuador. Photo: A. Roquero." from Ana Roquero (2008) Textile Society of America Symposium Proceedings Identification of Red Dyes in Textiles from the Andean Region above second: "Dactylopius confusus crushed scale insect, Fort Collins, Colorado, United States" from Wikimedia. below first: "scale bugs" on my houseplant, perhaps female Dactylopius confusus or Dactylopius coccus, from https://biology.stackexchange.com/q/108276/27918 below second: Structure of carmine from Wikipedia
It depends on the fluid in the blood, if it's more hydrogenous that oxygenated then you can use This to circulated oxygen(or any other gas that fits.) It would also (if hydrogenous) likely be similar to this, plus it would result in dark grey oxygenated blood color, and silver colored when deoxygenated. It would be ideal in a very dry environment due to the toxicity in water. In other words, it would have to be in a desert.
