Yes, a red lens will work as long as it does not "leak" white light from the sides (black tape can help here, I used pieces of opaque acrylic on one set up.
Be aware that the grills for water to enter the filtration area are subject to an octopus in the sump. The all-in-ones are very susceptible to this as the back area is an inviting dark spot. It MAY help to keep your live rock centered and off the back wall but placing a VERY coarse (to allow flow) sponge behind much of the overflow area may be required.
Be aware that the grills for water to enter the filtration area are subject to an octopus in the sump. The all-in-ones are very susceptible to this as the back area is an inviting dark spot. It MAY help to keep your live rock centered and off the back wall but placing a VERY coarse (to allow flow) sponge behind much of the overflow area may be required.