Yellow?

Yes, but quite often, plants with a high percentage of Sativa genetics can be more pale than their dark green Indica cousins. According to your diary, you have not fed them anything as yet, and while your garden soil may seem healthy, cannabis is what is known as a "gross feeder", meaning it needs a steady supply of nutrients to perform best. Now that your plants are starting to flower, giving them some type of supplemental feeding will be necessary if you are expecting to harvest some tasty flowers. There are a multitude of cannabis specific fertilizers now available on the market and purchasing some would be highly recommended and ASAP. At this stage I would be giving them a half dose of grow nutrients for the next two or three weeks, before switching to half grow and half flower nutrients, again at half strengths, for the following two weeks, before switching to straight bloom/flower nutrients through to maturity, also at half strength, this is ample strength for small plants in soil. Try and aim for a cycle of water/water/feed, so that your plants are receiving fertilizer every 7 days or so, and always at half strength. This should boost your plants' health greatly and ensure you will have some tasty flowers to harvest. Some of the easier to use nutrients that offer complete nutrition are Bio Vega and Bio Flores made by Bio Canna, Organic Grow and Organic Bloom made by B.A.C. and Flora Nova Grow and Flora Nova Bloom made by GHE are all excellent and require no mixing, just one bottle of each is all that is needed. They are all also highly concentrated, meaning one bottle of any of them will last multiple grows or many, many plants, making them economical in the long run. They may seem a bit pricy, but they are quality products with a long standing great reputation and have been specifically designed for cannabis and cannabis only. I can highly recommend them all, results over many years have been excellent and all are ideal for outdoor plants growing in soil. Hope this helps,............. Organoman.