If a cow develops a preference for eating white four o'clock flowers and ignoring pink and red four o'clock flowers, what type of selection is being demonstrated? Would the cow eventually eliminate all white four o'clock flowers from the population on which it feeds?

Directional selection; the cow would not eliminate all white flowers because the allele for white flowers is also carried by plants with pink flowers, which are not eaten. Crosses among plants with pink flowers would continue to create some plants with white flowers