Euphorbia plants don't like too much water, a mild sprinkle of water would do or you may just water your plants every 2 days or more depending on the climate and location of the plant. Placing your Euphorbia Milii under direct sunlight would make the coloring of the flower even brighter that's why it is a good practice to keep your Euphorbia facing South. Try using less compacted soil to drive away the water in less time. Choosing pots with enough holes in it would be a good decision because it would help in keeping the soil dryer especially whenever there's an excessive water in your Euphorbia.