The phrase "solid backgrounds" is correct and usable in written English.
For example, you could use the phrase in the sentence: "The website designer suggested using solid backgrounds for a clean look."
We came from solid backgrounds that kept us from those things.
His bold, blocky illustrations in primary colors, composed of simple, familiar shapes and set against bright solid backgrounds, somehow unleash inquisitiveness and imagination.
All five members — three Democrats and two Republicans — have solid backgrounds in labor law, which bodes well for bridging potential partisan divides.
Its walls and ceilings are decorated with different patterns stenciled onto solid backgrounds — an economical imitation of wallpaper used throughout the Head House — that have been scrupulously cleaned and repaired.
The designers need to use solid backgrounds, applying dark on light beats and light on dark.
As it happened, however, it was just at this time that a new tendency was emerging in nishiki-e, in the direction of a more painterly feel, eliminating solid backgrounds and bands of gradation for a lighter, more modern touch.
But Alonzo Stevens, the football coach at Vicksburg High School for 20 years, said Croom had a solid background.
There is a confidence there born of success and a solid background.
Lafcadio and Meursault play out their revolt against an all too solid background of convention.
Our course was M.I.T.-hard and needed a very, very solid background.
For Lane, the public "wanted a solid background to give some coherence to the newspaper's scintillating confusion of day-to-day events".
