Colourise texture on old hardware

Is it possible to colourise a texture on older (GF1 / GF2 era) cards?

More specifically, I’d like to take a 2d greyscale texture and apply a 1d colour gradient based on the intensity. Ideally the greyscale’s alpha would be left alone. I suspect I’m out of luck as this probably requires a dependant texture read (so thats what, GF3+?).

What about using palleted textures? It would work I think, but I don’t know how good support is for them (isn’t it being phased out?).

(Dunno whether this should be in ‘advanced’ or not though…)