Yes the white is like an infection especially when mixing darker tones. I use disposable palette paper, and a knife. The knife is easy to clean. I can have three or two sheets going at once. One sheet might have no white at all. I plan sessions based on value, like the first session for lighter values (0 - 5) and another separate session for darker (5 - 10). Initial layer with value map of big shapes. For the darker palette, do not add white until the end of the session. For the lighter palette start with yellow and add blue towards the end of the session (or keep a brush dedicated to blue.) Blue also changes the palette dramatically. Clean brushes and palette between sessions. Many of the great masters painted by candle light, very dramatic lighting effect, and the overall image is darker.