He means that image is multiplied with a color.

Here's discussion about improved undelphix and how it can be done:
http://www.delphigamedev.com/forums/viewtopic.php?t=292

It makes this kind of command possible:
[pascal]DrawAlphaCol(Surface, DestRect, PatternIndex, RGB(0,255,0), Alpha);[/pascal]
That would draw grayscale image as green, red or blue image as black and so on...

Edit: Made this small demonstration
This uses only 1 TDXImageList item, only colors them with alpha weakening when going down.