I'm not a fan of solid-front harnesses. Get a cheap one and try the basic configuration, you'll see why I like a split front. But you are right, the use of a chest rig with a few big pouches is great with a pack- and you'll find the pack probably feels a little more natural with the stuff hanging out in front, but if you aren't careful you'll turn into the Stay Puffed Marshmellow Man. *grins*
As for color... There are custom makers out there. I've spoken with the gentleman who runs
Black Ops Tactical Nylon about a custom pack I was thinking about, his rates are reasonable, but I'm not sure if he does bright colors normally. (I found a really good deal on the production pack I was also looking at, and had the pouches on hand to rig it how I wanted, so you might not want to mention my name *blush*.) When Doug designed his aviator's kits, he went with an outfit called Semper Paratus Tactical for the pack, they should be able to do it. It will take some looking, but it shouldn't be too hard.
However, custom gear is often expensive gear. MOLLE gear, by definition, is covered with lots of webbing points. Getting someone to make you up high-visibility panels that you can attach is easy, it is just a little webbing, some bright cordura, some snaps or velcro, and thread. Anyone who can sew can make them.
If you want to see what the rig I use looks like,
click . Retrofiting signal panels to the front of the main pockets would be easy enough, as you can see.