I would look for the cause of the foliage problem, cutting it off will not help. Your boxwood is spaced too far apart to succeed in concealing your hose reel. I would add three more plants in the space in front of the hosereel. Al

Many varieties of English boxwood do tend to change color in summer, nothing wrong with the plant. Many varieties of Japanese boxwood tend to bronze up in winter. If you prefer a boxwood that stays deep green year round, you should replace it with a variety such as the Japanese Boxwood, Buxus microphylla japonica'Green Beauty'. English Boxwood/Buxus sempervirens tends to not do as well in hot summer areas, better near the coast.

I actually prefer to use the different plant, African Boxwood, or Myrsine africana, because it is just as drought tolerant, but a uniform deeper green and also faster growing.

Ultimate size of boxwood at maturity will easily cover your hose reel with just the two plants, but it could be quite a wait. I've seen boxwood get tree sized in 40 year old plantings. Clipping regularly is preferred where you want a denser, tighter habit, if you are just looking for fastest height, leave it alone until it nears the size you want.