Script to replace all pixels of a color?

I know we covered it before but I can't find it...

I think we already covered it but I can't find it... maybe it got archived...?

Anyway I'm looking for a script that will allow someone to pick two colors, and replace every pixel matching the one with the second color. Like "replace all pixels of color #369 with #471" or something like that. Anyone know where that script went, or willing to remake it? Thanks in advance.