Summarize:

Keep your mixing time to no less than 1 minute and no more than 2. When plaster isn't properly mixed, it has a tendency to separate. On the other hand, overmixing can cause bubbles to form, which may decrease the strength of the plaster or ruin the smoothness of the finished wall. Perfectly-mixed plaster will be opaque, creamy, and free of lumps, bubbles, or grit. A splash of vibrant color can make walls pop. Stir dry powdered pigment into a container of water to create a slurry, then add the slurry to the plaster bucket just prior to mixing. This will make for effortless blending and help you sidestep common issues like spotting and clumping.  When incorporating pigment, you can add up to 10% of the total weight of the plaster you used, or until you reach the desired depth of color. Colored plasters allow certain paint shades to show up better. For instance, royal blue paint will stand out boldly over a blue-tinted plaster base without the need for as many coats of paint as you would need for plain white plaster. They can also be quite attractive on their own, providing a more earthy, natural look to a room. right away. Once it's been mixed, pour the plaster onto a damp spot board to prepare it to be scooped onto a hawk. Depending on the working time of the plaster, you'll have somewhere between 5-45 minutes to get it onto the wall before it begins to harden, so don't delay. For best results, always mix your plaster just before you smooth it on. Plaster spreads and sticks best when it's fresh.
Avoid under- or over-mixing. Add pigment for bolder colors. Apply the plaster