For those new to home theater projectors let's start by painting a picture of what Brilliant Color is, and why, etc.
Brilliant Color itself is something that Texas Instruments, the makers of the DLP chip, have been offering in their chip sets for many years. It enhances a number of features such as saturation, contrast, and who knows what else, in order to improve the image. What is perhaps most interesting is that TI presents Brilliant Color as something that each manufacturer can customize in their projectors, even use it differently in different DLP projectors from the same manufacturer. Some projector companies utilize it, I believe, without using the Brilliant Color name, they just incorporate that into their image processing, with or without a fancy name.
In earlier days it was not uncommon for a projector with Brilliant Color to have multiple choices. But these days, more often, it seems to me, projector manufacturers offer Brilliant Color as an Off, or On choice.
Not so, in the case of this Optoma HD131Xe. They offer a sliding scale from Off (0) to 10.
Since we see this as a home entertainment projector, and Mike only calibrates one mode, he left it on 10, because that setting provides the brightest image, and we see this projector, mostly going into rooms that are less than ideal, and need the brightest image.
The first three images in this section show you some different settings on the 0-10 scale for Brilliant Color. It's relatively subtle on these dark images, but look at the light (yellowish) from the large windows in the building, look at the detail and perceived sharpness of the roof to its left. You'll also find in general, some fine lines that stand out more with the higher settings. The last three images - of Captain Kirk, in order are Brilliant Color at 10, 5, and Off.
When looking at Kirk, look at his forehead and left cheek for image noise, also the light blue vertical structure on the right. For contrast/perceived sharpness, look to his uniform collar and the stitching below.
Bottom Line on Brilliant Color: First, Mike says grayscale balance is as good with a setting of 10 as lower numbers, usually better. Consider Brilliant Color to be a tool to use to get the image to look the way you want it to. The more you use, due to contrast increases, etc., the less natural the image, but if it pleases you, go for it. You might want to remember, though, that BC off will cost you more than half your total brightness (see the chart on the Performance pages of this review.
Remember, this is an entry level projector, there are lots of picture quality compromises. You can hold out for perfection in your next projector - which if DLP, you can leave Brilliant Color turned off. I do like it, though, having multiple settings. Often the maximum is way over the top, on some projectors, so if their choice is Off or On, then it's without, or over the top, as your only two choices. I'd say the Optoma HD131Xe projector has a very good Brilliant Color implementation.