This is a nice idea!
However, another option would be something like:
@startuml
:
|= ColorName|= ColorName|
|<#AliceBlue> AliceBlue |<#Beige> Beige |
|<#AntiqueWhite> AntiqueWhite |<#Bisque> Bisque |;
@enduml

Would it be possible that you complete this tiny example with all colors ? It would help.
Or another option is that we implements something like:
@startuml
colors
@enduml
That would print a nice color palette.
What do you think about it?