Leaves turning color start of Bloom

Hey, if you've over-fertilized, I would measure the runoff to check the pH and EC values; these shouldn't exceed 2 for EC and the pH should be between 5.7 and 6.6. If all that is fine, it could also be a deficiency of micronutrients like zinc or iron. Another thing could be that they are stressed from heat and light; measure the DLI or PPFD with the app called Photone at various points on the plant. I hope this helps you a bit.