Well, any element (or, indeed, any molecule) will emit a characteristic pattern of spectral lines when heated, so colored flames are pretty easy to do. Sodium, for instance, gives a bright orange flame, as seen on the left side of this page.
Colored smoke is more difficult, since the same reactions responsible for combustion also tend to destroy organic pigments. However, this Wikipedia page lists several pigments that are heat-stable enough to work. Most of them are at least somewhat toxic, but Disperse Red 9, Disperse Red 11, Solvent Red 27, Solvent Yellow 16, Solvent Yellow 56, Solvent Blue 35, Solvent Blue 36, Solvent Blue 5, and Solvent Violet 13 are not (or, at least, their Wikipedia pages say nothing about toxicity). So if you want to have a plant that burns with colored smoke, those are probably your best bets.
Also note that compounds that are already fully oxidized can't be oxidized further. Most metal oxides, however, have fairly dull colors. Iron (III) oxide, for instance, is kind of a reddish brown (rust-colored... because it's rust). However, in order for a material to have visibly rust-colored smoke, whatever's burning must have quite a lot of iron in it, which isn't likely to happen in an organic plant.
In any case, here's Wikipedia's list of inorganic pigments, if you need more inspiration. Just stay away from the ones with toxic heavy metals.