REI is a national chain with a huge budget for market research.

If most of the bikes on their sales floor are matte black, it's because most of their potential customers are more likely to buy a matte black bike than any other color.

It's not just the whim of one of their wholesale buyers who woke up one morning and said "We're going with black because that's my personal favorite"

I guarantee they did a metric ton of research to determine that a matte black bike will sell faster on their sales floor than a blue or yellow bike.

And that doesn't necessarily mean that research tells REI that people are walking in specifically looking for a matte black bike. Just that they are more likely to walk out with one.

Here's a couple reasons why matte black might sell better at REI...

1) A large portion of the population is legit into matte black right now. Color preferences and trends do change every few years. (For everything. Bikes, clothes, cars, etc) Matte black may just be really popular right now.

2) Matte black makes REI bikes look more expensive than Wal Mart bikes. Despite it's fancy displays and niche gear products, REI is still a big box retail store at it's core. And MOST bike shoppers aren't super educated rider. REI's customers aren't overall more bike savvy than Wal Mart bike shoppers. But REI shoppers are likely able to spend more than Wal Mart shoppers. It's got to do something to make it's bikes more attractive to a consumer than a Wal Mart bike to justify the higher price tag. Wal Mart bikes are all neon yellow and green. For a while those stood out and looked high end to the untrained eye. Now day-glo bikes are everywhere so places like REI are shifting back to matter black to be different than the neon bikes. Soon Wal Mart will carry more black bikes to give the untrained consumer an option fro a bargain on an expensive looking bike. In 5 years Wal Mart will have all the matte dark colors and REI will have neon rainbows in the bike section when that trend reverses.

3) Black is more neutral. You can make a black bike look red or green with accessories. A green bike is a green bike. It makes 1 bike more interesting to 5 buyers.

4) REI has made a huge marketing blunder and bike sales will tank. (I'd bet heavily against this option)

5) Matte black doesn't sell better, but it reduces the production costs thus improving the overall profit margin on each bike. (I doubt this is the driving factor. But it might play a part)