If i understand you correctly, you want to color the Set Number 8?
Sadly this seems not to be possible over the UI. Can you please report this as a bug on Sourceforge?
I looked a bit into the code, but was not able to determine how coloring works exactly.
I found out, that scintilla has 255 styles, and for example style 0 ist the default background color.
Codeblocks overrides this styles in the configuration file with the xml path: editor/colour_sets and then in the tags <styleX> where X is the style number.
I was not able to find out, what style number the keyword set 8 has...
What i found out is, that, when the keyword is in the middle of a comment section of the code, than the styleX+64 is applied. For example numbers have the style nr 4, if they are in a comment section they have the style 4+64=68
maybe some other dev can help you...