I've not yet tried the "new" Ektachrome, but have a large frozen stock of the "old" Elitechrome and Ektachrome 100 variants which I am working my way through.
Latterly I have noticed a tendency towards a definite blue tint in outdoor conditions (due no doubt to the age of the film) and found that adding a warming filter, 1A or 81A and even 81B, has restored a pleasing color balance particularly with sunny blue skies. I've always felt that a slightly warmer result looks better than an excessive blue tint ( IMHO ), so personally I would certainly use a 1A skylight.