Color accuracy of a display refers to the display's ability to accurately reproduce and display the source signal it receives from your system's GPU. It is typically evaluated as an average score across a spectrum of colors ("gamut") within the defined color space used for the evaluation. 

There are a few widely used color spaces for monitor color accuracy evaluation, but sRGB, Adobe RGB, DCI-P3, and Rec. 2100 are the most common. Each color space covers a certain gamut, which can / will overlap with gamuts from other color spaces. Most monitors are produced to accurately reproduce the sRGB color space as accurately as possible, but sRGB still only covers 33% of the visible light spectrum. Monitors specifically advertised for color accuracy are typically evaluated over a more comprehensive color space, such as Adobe RGB (~50% of the visible light spectrum) or DCI-P3 (45.5%) color space. "Good" color accuracy measurements typically sit above 90% fidelity to the evaluated color space eg. "95% sRGB", with higher fidelity being better.