Vacations

White or Yellow muppets have nothing to do with leagues. Its only available (yellow) or unavailable (white) for clanchallenges.

Please provide more information yelmboys, like: who are the 6 members you wish to add?

To be able to enter members in the league team their league shield (displayed on the same muppet that can be either white or yellow) should be set for your clan. So at this moment you cant add jdennisd, because his leagueshield is not set for your clan.
I hope you are not trying to add yourself to the team either, since you are the only one on vacation of your clan at this moment...