There is some inconsistency in the control of style properties via skinparam parameteres. One consequence is that there seems to be no way to replicate the look and feel of the deprecated BlueModern skin using skinparam.
Consider this example:
A -> B: ping
B -> A: pong
The skinparam "SequenceGroupHeaderFontColor" apparently controls both the color of "loop" and "forever" in the above example. There seems to be no way to give the two elements different colors.
Compare this with the situation with "SequenceGroupHeaderFontStyle" and "SequenceGroupFontStyle": the two properties separately controls the font styles of "loop" and "forever".
Also, while the background color of the loop box header (i.e. that of "loop") can be controlled using the "SequenceGroupBackgroundColor" property, the main portion of the loop box is not affected by the setting of the property. It seems that the only way to change the background color of the main portion of a loop box is by using "BackgroundColor", but sets the background color of everything else as well!
Please fix the inconsistency. Many thanks!