Theres a decenty potent purple predominantly sativa strain called purlple white widow (an oxymoron, huh?) and it's a purple power/white widow cross, and I would say it tops out at about 15% THC. Purple power itself only tops out at about 10%, and white widow at about 20%. Buyer's beware tough, it's white half the time and purple the other half. My buddy got a 10 pack and got 3 purple girls and 3 white bitches. It also grows like a weed [
] so it gets big and is a very tough strain, so I would keep this in mind.
Also, you could go with a classic blueberry. Better for indoors, but is better for a grower with a few grows under their belt. If you do go with blueberry, make sure to top/fim it. Blueberry's full potential yeild can only be realized by doing this.
Also, color's in strains show it two ways: in the leaves and in the calyxes. It's a lot easier to get one where the color starts in the leaves, but the strains where the color starts in the calyxes are usually a lot better and have the color in the final product.
Good luck, growing and finding a true colored strain