Added an image with a room that includes a window, outdoor lighting. Cloudy day.
The indirect light almost reflects more of the matte finish giving it an even whiter, almost whitewashed look. Although the semi gloss can provide more reflections, the matte finish still has a sheen that does the same. However, when you get a less reflected light, you see what you see now; the semi gloss really stands out, makes the grain and colours just pop!

[Linked Image from i.imgur.com]

"Those who preach the myths of audio are ignorant of truth."