Sprite color convertor?

What's the fastest way to recolour a sprite set? I just want to replace some tones of black with some tones of yellow and reds instead of grays. Is there any program that can do this automatically, or do I have to paint pixel by pixel?

SLADE3 can do it with palettized sprites. Select the sprite lump(s) you want to recolor, and use "Graphic -> Color remap" feature from context menu.