I have an idea for this crazy blood thirsty monster and the reason behind its love for killing is red is the only color it sees, but I don't know how or if that is possible a logical scientific explanation would we nice. I haven't seen any data on creatures who see in black and white plus another shade of color. Please help, and thank you!
People see 3 colors (red,green and blue, more or less) when seeing in bright light (cones) and black and white (rods) in low light. Your monster, if it only has cones which respond to red will see the world in terms of redness. However, since her bright-light color experience is only in terms of red, she would not develop the concept of "red" vs "white". So her visual perceptions would simply be bright or dark (or shades in between) which would correspond to the amount of red in the objects she sees.
An animal with panchromatic vision plus one color channel could use several different possibilities.
It could be a narrow filter looking for a specific peak that highlights a specific feature it uses to hunt. Maybe ripe fruit lights up for it to find, or it sees blood from wounded animals to follow and track down.
So, imagine a b&w picture with a specific color (only) painted in, when it is above a certain threshhold brightness relative to the overall brightness.
Some birds for example easily spot urine trails left by mice, as their filters are designed to separate that from the grass color. But that's not the only thing they see, as they can have extrodinary color vision in general.
Alternatively, the single color channel could be a broad-band filter, sensitive to about half the visible spectrum. This is combined with the panchromatic image not to make a distinct perception of redness, but to improve contrast in general. Look at old b&w photos shot with different strongly colored filters, if you've studied such things. The picture is still b&w but indistinguishable objects become different now. In particular this technique affects the sky.
The brain and optic processing could use both filtered and unfiltered forms for edge and feature detection, so he's not aware of any concept of color at all, but can see different objects that are the same brightness and would blend together otherwise.
Perhaps dogs see the world this way. If this is what you're really thinking about, then consider that if it did occur as described it would not give the possesser same mental concept of seeing a color.
Now the particular choice of red makes one wonder though. It is thought that we evolved the red/green channel last. The blue/yellow channel is useful for normallizing object's appearances over the course of a day and between sun/shade, so even without a perception of color as an attribute it allows the eye to calebrate for color temperature.
Some animals have separate organs for infrared. Pit vipers for example, and shrimp that live close to thermal vents. Maybe a near infrared channel meant originally for detecting heat can also see into the range we woukd call red? People interacting with that creature would note the red sensitivity and be unaware of, or think it separate from, the heat sensitivity.