Hi Afsheen, One easy way to do this sort of thing (if you don't mind a little IDL programming) is to assemble the image in the HSV colour space. Put your backdrop band as the V (intensity) band, construct an H (hue) band from your overlay band, and make up an S (saturation) band that's 1.0 where you want your overlay band to show and 0.0 where you don't want to show it. Transform this lot to the RGB colour space using IDL's COLOR_CONVERT,/HSV_RGB and give the result to ENVI using ENVI_ENTER_DATA or ENVI_SETUP_HEAD (after assembling the 3 RGB bands into a 3D BSQ array if in memory or writing them to disk if not). That's the general idea. A bit more on making an H band... In HSV space, hue values go from 0=red to 120=green to 240=blue, then through purple back to red=360 (== red=0). If your overlay band's just boolean (a mask of 0 and 1 values) then simply pick the hue you want and multiply it with your overlay band. If it has a range of values then either threshhold it to a mask for a single colour, or scale it to the hue range that you'd like (0 .. about 270 is a common choice). There are other things that you can experiment with in the HSV colour space, e.g., rescaling the intensity and bumping it up with an offset where the overlay band is valid, or varying the "amount" of overlay shown by adjusting the saturation values.