If I want colored contacts. I have astigmatism, and the bc and dia is lower, will that effect my vision?

No. Base curve (bc) has to do with the steepness (or flatness) of the contact lens. Special soft contact lenses called toric contact lenses are required for clear vision in people with significant amounts of astigmatism. They are required to stay 'tighter' on the cornea and this can be accomplished by a steeper (lower) base curve and a smaller diameter (dia). Visial quality isn't affected.
No. There are colored contact lenses that have power and no power. This has nothing to do with bc or diameter--these correlate to how the contact fits your eyes. Astigmatism can affect the vision, if its significant and the color lenses have power. Just remember, contact lens, colored or not, is a medical device that needs to be fitted by trained professional. Ulcers and loss of vision can occur.