I am guessing you are showing at the lower levels - Intro through 1st. For those levels there is no requirement for white breeches even at regular shows, although that is certainly the most prevalent option. Keep your saddle pad simple - white or a solid darker color are best. Gloves can be white or a single dark color.
If you can, ask a friend, your trainer or even the show secretary what the typical turnout is. Schooling shows vary and the show secretaries I know are really helpful and want you to have a positive experience, so don’t feel weird asking. One series near me has lots of riders in paddock boots and half chaps, tan breeches and a polo shirt. Light tan breeches and a collared shirt (polo, sun shirt, show shirt you would wear under a jacket) would be perfectly acceptable in most schooling shows.One show series near me is a bit closer to a rated show and many of the riders are in white breeches and coats and some even braid manes. Even if it isn’t required, you will feel better if you “fit in” and look the part.
Oddly enough dressage is starting to come around to variations in color and style. I was comparing notes with a friend who rides jumpers and her trainer (who also does hunters) wouldn’t let her get a new blue jacket to show in. Meanwhile, I saw lovely grey, blue, brown, purple and black coats with varying amounts of bling on coats, pads, boots and browbands at the last dressage show I attended.
Some other tips that may help you. Spend a bit of time memorizing your tests, even if you will have a reader, as it will help you in the ring. Focus on rhythm, well-placed turns and the size and shape of your circles. If you make a mistake or have a bad movement, take a deep breath and let it go - ride the next movement. SMILE and have fun!