I found this when searching for what color is &H80000018&

The &H indicates that it's a hex code. Hexadecimal digits range from 0 to 9 and then A-F (for 10 to 15)
The next 2 digits specify "Red" between 00 and FF which is 0 and 255. (128 in the case of the code mentioned above)
The following 2 digits are "Green" between 00 and FF which is 0 to 255 (0 in this case)
The following 2 digits are "Blue" between 00 and FF which is 0 to 255 (0 in this case)
The last 2 digits before the closing & indicate the transparency or "opacity" from 0 to 255 (24 in this case)

According to that, &H00C8FFFF& is RGB 0,200,255 at transparency of 255

This site is old but may be of some interest to you.