Beginner Gardening: What's wrong with my cacti???, 1 by SemiGreenThumb

SemiGreenThumb wrote:
About one week ago I transplanted my cacti (3 in one pot). I also moved the pot outside to see how it would do with more sun light. Now I am noticing that the top third of the cacti are losing their green and are turning more like whitish-yellow. I don't know what this means. Are they dying? I only water them once per week, when the soil is dry as far as I can stick my finger. How can I revive my cacti? Please help!