What is the best time of day to take a drive through the park in order to capture some of the best color? Thx...

Early am or sunset, agreed.

Either early morning. Or going into sunset. very nice ride to the top of the mountain and back down

It depends which colors you like. Sunrise, sunset or during the day to play with the sun. Make sure you have enough water with you.

Twilights!

Sunrise or sunset also helps with the heat if you're getting out to take some shots