Yes, having matching colours gives you a +5 in defence, though having all different colours gives you a +6 distraction bonus, lowering your opponent's ability to react. Pink gear gives you +10 in manliness through what's known as the Gene LeBell effect.
Seriously though, unless you're being photographed or video recorded as part of some big promotional event (HBO's 24/7, UFC Primetime or something along those lines), I don't think colour should matter as long as the gear does the job. Don't bypass certain brands because they don't fit the colour scheme you're going for. The best boxing glove in your budget might not come in the same colours as the best headgear or no-foul protector. One might be olive green with black, while the next may be blue, while the third may be red. Look around, find the best deals you can and go from there.
The first question you should ask yourself is what your budget is. Remember, you will eventually need:
1 pair sparring gloves **
1 pair bag gloves
1 mouthguard **
1 headgear **
1 groin protector **
2-3 pairs of hand wraps
** = only needed once you start sparring
If you're doing straight boxing, you'll also need boxing shoes, if doing kickboxing, you'll need shin guards.
If you're just starting, you likely won't be sparring right away, so you can start with bag gloves and hand wraps. Get the rest as you need.