Since you are going to use the light shirting to alternate each flower ... stick with using all of the light colors in the centers and all the dark colors for the petals. That will highlight each flower.
Depending on what you use together, some of those lights may look like darks for petals. Play each of them against each other and against the shirting background. For example, the flower to the far right and top has a petal on the top right which is a light shirting - it just gets lost against the shirting. That one would definitely be a center. But some of the other "light" petals you have could remain as petals or be centers.