Daffodils-when to split up, color change cause?

When is the best time to move and or split up daffodil bulbs? What would cause yellow ones to turn white? They are in the same bed but in a different corner. They were planted at the same time, the first year they were all yellow, second year 3 of them turned white.Daffodils-when to split up, color change cause?You can divide daffodils any time after the tops die back until mid-fall. The white ones have been cross-pollinated.