doc/user/README.moreColors (in konsole's source) says:
"The separator character 03/10 they use is a colon, not a semicolon... I wonder 
if the xterm implementation was based on an improper reading of the standard?"

Indeed, it was a bug in xterm, fixed in patch #282. Also, iterm2 added support for colon separator: https://code.google.com/p/iterm2/issues/detail?id=218

SGR escape sequences that set a 256-palette color (38/48;5;index) or a true color (38/48;2;red;green;blue) should also accept colon as the separator (according to the standard), in addition to the buggy-by-design semicolon (for compatibility with older xterm and with terminfo entries for 256 colors).

Reproducible: Always

Steps to Reproduce:
$ echo -e '\e[38;5;100;48;2;40;60;80mabcdef'
$ echo -e '\e[38:5:100;48:2:40:60:80mabcdef'

Actual Results:  
First one works, second one doesn't.

Expected Results:  
Second one should do the same as the first.