Of course you want to reserve your brightest, purest, most saturated color for your focal point, but sometimes it seems that you just can’t get it bright enough. Well, put down your brightest color for your first stroke. Then every other color after that will be less saturated.
For instance if you have a little bit of red in the painting, The brightest red that you will be able to get will be cadmium red, maybe with a little yellow and white added to it. You can’t get one brighter than that. If you put your cad red down on the canvas, then you know that all other reds in the painting will not be as bright as that one spot.
If you go from the duller reds building to the brighter, you may find yourself with nothing left to work with to get anything brighter.