UserList is a list of dictionaries, like:
UserList
[ {Name:\"Alex\",Age:25}, {Name:\"Peter\",Age:35}, {Name:\"Muhammad\",Age:28}, {Name:\"Raul\",
Something like this should do the trick:
var i = 0; var l = RowColorList.Count; UserList.ForEach(user => user.Add("RowColor", RowColorList[(i++) % l]));
The % operator will guarantee "cyclic" access to the RowColorList.