That's a DAC with a RAM feeding its input through a translation buffer that's built in, such that it "sees" a value and uses that as an address to its, say, 256-byte buffer on each color. Whenever a value from external video RAM is written to the DAC, it flows through the translation buffer producing the color value that was written to the buffer rather than what was in the video memory buffer. That's what's found on most video boards of the early '90's.

RE