According to Dorothy Rainwater in "American Silver Manufaturers", page 77, Holmes & Tuttle Mfg. Co. was founded in 1851 by Israel Homes in Bristol, CT. They made plated knives, forks and spoons. The company was taken over by Bristol Brass and Clock Co. in 1857 & operated as their silverware department until 1901 when it became the American Silver Co. which was bought by International Silver in 1935.
Since they appear to have been maker's of plated ware and your spoon is not marked Sterling or 925, there is no reason to believe that it is other than silverplated. The goldwash is not unusual on flatware. If your piece was not misused and it is heavily plated there is no reason the base metal should be showing through. Also, if the base metal is a white metal, it is often difficult to see. Hope this helps.