If my legend is Viktor, can I use cards of colors other than blue and yellow (e.g., a purple spell without a recycle cost)?

Ruling: When Viktor is your legend, you are restricted to only blue and yellow cards. You cannot use cards of other colors, even if they don't have a recycle cost.

Nuances:

• You can build a deck using only blue cards with no power costs and run 12 yellow runes as a valid deck construction strategy.