How to see Mars and Venus in color? My telescope is Arsenal - Synta 70/700 AZ2 (refractor model). 140x max zoom (10 mm with Barlow).
I could clearly see Jupiter and Saturn in color. I even saw brown stripes on Jupiter.
Yet, when I tried looking at Venus and Mars they appeared pure white, totally washed out by the Sun. I was observing about hour before sunrise.
Is there a way to see them in true color with my current tech? Maybe they could be seen only at certain dates? Or maybe I need some filters?
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).