I think that the Colt 45's colors also were navy and orange.
Correct. The .45s and the original Astros color schemes were identical (and damn good looking, in my view). In the early '70s the scheme changed from predominantly navy with orange trim to predominantly orange with navy trim (a mistake in my opinion then and now). The logo and graphics stayed the same, only the color scheme was reversed.
Then came the rainbows, shoulder rain, blue & gold and brick and sand.