In your graphic design program see if you are using RGB or CMYK color profiles.
Then call the copy place and ask them what profile their machine prints in. i believe most printing shops use CMYK. If your design software uses hex color codes for RGB you can use this online tool codebeautify.org/hex-to-cmyk-converter
Just copy and paste the link because when I try to embed it I keep getting errors when i click the link
I had the same problem but with concert posters. I do all my artwork in Gimp which uses RGB, The local printshop that can make large format prints like 11 inches by 17 inches uses CMYK. So every time i took my files there to be printed they looked fine on the monitors, but when they would print out of the machine the colors were always off. I got tired of this ALWAYS happening and having to go and convert my files to their color profiles then return to re print so I bought a $30 color printer from Walmart that will do CMYK and RGB. Of course the printer was cheap but an ink cartridge costs twice as much as the printer.
hope this helps
make them loud enough to melt the sun