Ah...striplights. If they're Zip Strips, T3's, or anything else than
R40's, they probably don't have glass roundels, but if they're
R40's, which they probably are, they probably have some combination of
no-color, red, blue, green, and amber. These are thick glass color filters that are fitted to the size of the slots in the striplights, and are designed for three or four color mixing, such as
RGB, RBA, or RGBA mixing. Some of them also have a
no color (no filter or
clear glass) for
no color toplight. There's standard roundels and beam-spreading roundels, the beam spreading ones have a pebbled surface and
convex area on the side that faces out to diffuse the light and make it
cover the
stage more evenly. While
R40's are hardly spec'd at all for facilities these days, they many times come with roundels because of the practicality of gels
never burning out. We have thirty year old ones in my HS theater that are still just about as saturated as new ones (yup, I compared them with new ones, but didn't have a light
meter, so it was just a visual test).
So no, if they're old, probably not gels. But if they are gels, you're lucky, and you can just
switch 'em out. Otherwise, I'd advise the color mixing route. Roundels are
really, really expensive to buy new.
My rule about followspots: if it isn't a musical, don't use them at all. Some people may not agree with me, but there is almost never a need for them in a regular
play.