Colors for Blockland colorsets use the Red/Green/Blue/Alpha (transparency) format, either in 0-1 or 0-255 format for each colour.
The Red, Green and Blue numbers just need to be
converted to this format, you can use any Internet converter. The Alpha number defines the transparency - 0 is invisible and 1 (or 255) is fully visible, which you should use for most standard colors.
For an example of how to set out the colorSet.txt file, look at the default one in config/server. If you have RTB and wish to upload the set to their server, then you will need to package it in a Colorset_*.zip folder, including a description.txt file with it.