@Heather Suarez Prepare for a long reply from me because this subject is very complicated and I'm very thorough.
Along with strong light and low water, temperature plays a very important role in color as well. I'm an outdoor grower, so much of the coloring in my plants solely depend on California's flunctuating weather. I've noticed when temps reach 75F or more, echeverias start to open up and green more as if to soak up as much energy to grow faster. My aeoniums, on the other hand, close up and deepen in color as they go dormant during the heat. We had high temps for several days at 85F+, and then all of sudden it was cloudy and at 69F for two days in a row. Boy, did it wake up an array of new colors for most of my echeverias. The wintertime is the best time to get those colors to pop, especially when you mix it with strong direct light and low watering.
It's possible to maintain stress colors even during the warmer months (although trickier and depends on the variety). For example, many Dick Wright hybrids like Valentine, Silveron Red, Petticoat, Jane Naylor, etc keep stress colors with lots of light and warm temps. I give them 10+ hours of direct sunlight, and protected under a white 50% UV filtered shade when temps reach above 75F. A strong source of light for many hours a day plus a period of drought can cause some to stress just like they would during the winter. So, if possible, increase the amount of hours of direct light and, like Christy said, reduce the amount of water. Experiment with caution though! Learn from my mistake and don't combine strong light with low watering and high temps or it can boil the plant from the inside and rot! At high temps (75F+), they need some protection from harmful UV rays if they're not heat resistant.
Lastly, if you want the exact science to this madness, you can check out a very helpful article about photobiology. It talks about how changes in light from season to season can trigger a chemical response in trees to accumulate anthocyanins (red, blue, purple pigment) then combined with low temps, cause them to display the anthocyanins to protect the plant from frost. I believe a similar theory applies to succulents as well. In other words... very complicated to replicate out of dormancy season 🙈 Here's the link: http://photobiology.info/Chalker-Scott.html
Sorry for such a long response! I'm quite the talker when it comes to this kind of stuff.