The RGB color model for HTML was formally adopted as an Internet standard in HTML 3.2, though it had been in use for some time before that.
The web-safe color palette consists of the 216 (63) combinations of red, green, and blue where each color can take one of six values (in hexadecimal): #00, #33, #66, #99, #CC or #FF (based on the 0 to 255 range for each value discussed above).