I had similar questions on a new building project. I couldn't see enough difference in the frame designs to worry about, so the primary concern was keeping the same color of windows throughout the home. The window companies were glad to give small color samples for comparisons.  My research taught me that there were primarily 2 colors of vinyl windows on the market: white and almond, with very limited variations. The reason for the limited choice has to do with thermal expansion, as color tinted vinyl windows result in too many warranty claims. (Wouldn't it be nice get brown, or wood-toned vinyl window frames?)

I went with 3 different window manufactures, got the function I wanted and saved several hundred dollars. I chose frames that all had a similar exterior reveal (similar frame widths). Most of the interior sides of the windows were covered with curtains or blinds. After installation, I never gave any thought to the slightly different window frame designs. Nor did I ever hear any comments about the window manufacture mix, just comments on the nice light.