For example a bitmap has a red circle with black background
color, is there any way to change it to green from red in game?

pixel_to_bmap doesn't help too much since I've to specify each
pixel position precisely.

Any suggestions?

Thanks.

well, i do this with models that i want the same model but differnt colored highlights.

the areas to be colored i make white on the image/skin

just set a material to change its emissive and specular red green or blue values
might have to adjust the power as well for your needs

this works fine with models, sprites and even d3d automaterial ( level geometry texturing)

if workign with like a panel image you may be better off just swapping images vs trying to manipulate the image itself ( for speed and effort wise just faster).

Using paint shop pro you would not need to create them you chould just change the color of an existing image and save it. takes about 30 seconds if that.