The below code creates a signature that changes color depending on what time of day it is. While the markup is large the output is small due to the substitutions.

Signature code

[[User talk:Chillum|<b style="vertical-align:20%;text-shadow:0px 0px 4px blue;font-size:60%;color:rgb({{subst:#expr:256-({{subst:#time:U}}mod86400/86400*256)round0}},40,{{subst:#expr:({{subst:#time:U}}mod86400/86400*256)round0}})">Chillum</b>]]