Is it possible to put runes in the rune deck with a color not matching the legend?

Ruling: No, you cannot put runes in the rune deck with a color that does not match your legend.

Nuances:

• TF (Twisted Fate) could work in sealed/limited formats that permit 3 color decks
• In constructed, TF will have more play options in future sets with new legends
• Since TF is purple himself, he can currently only use 1 of his 3 abilities unless 3-colored legends are printed in the future
• Future legend options may allow building around which 2 of 3 of TF's abilities you can use