Hi Mary, you did not mention where you live but often a yellow rose will turn white due to heat and direct sun. Perhaps some protection from the afternoon sun will keep your rose yellow. As for the  crepe myrtle, these trees bloom best with no fertilizer and infrequent but deep watering. They also flower on new wood so prune in late winter to encourage new growth and to get rid of any weak or spindly branches.  If you prune too late in the spring you will be pruning off the flower buds. They also need plenty of sunshine. Try these tips this summer (no fertilizer, rarely water and no pruning at all except to remove thin branches in late winter) and see if next spring you are rewarded with some flower buds. Keep growing, Marianne Binetti