FBTS uses a formula based on the main -- or primary -- color of a plant's flowers to identify similar plants. The foundation of our analysis is the internationally standardized color system published by the U.K.'s Royal Horticultural Society. 

Each RHS color has a common name and a code combining a number and a letter from A to D. Immediate family of a color share the same number, but not necessarily the same common name. For example RHS#44A is Vivid Red, whereas RHS#44B and #44C are both commonly called Vivid Reddish Orange and #44D is Strong Yellowish Pink. Moving up one closely related color set, you find Vivid Reddish Orange RHS#43A and #43B, Deep Yellowish Pink RHS #43C and Strong Yellowish Pink RHS #43D. Moving down one closely related family, you arrive at RHS#45A to C, all of which are called Vivid Red and then RHS #45D, which is Strong Red.

Extended family can be so confusing! Don't worry about keeping the RHS common names and codes straight. Just be aware that all the plants in this gallery are part of one big happy color family.