How to see Mars and Venus in color?
You are seeing them in color, it's an issue of the mechanics of your eyes.  Eyes are made of rods and cones, cones seeing color, rods seeing greyscale.  When you are looking through a telescope, your eye adapts to the low light conditions and the rods dominate the sensitivity.
Jupiter appears much larger than both Mars and Venus, so your eye does not adapt as much and the cones relay more information, allowing you to perceive more color for both it and Saturn (which is also larger than both Venus and Mars in our sky).
That said, Mars through a telescope, to me, appears a bright orange.  Venus, to me, is indistinguishable from white, though it should look more of a pale yellow since that is its color in visible light.
You could try looking when the sky is darker, for Mars is visible in the middle of the night.  It's possible that the blue of the sky is affecting your color perception, too.  Venus is always a morning or evening object, so you should try looking at it just a little after it has risen (looking at it just as it rises will result in atmosphere issues).