@shiva002,
The color property accepts RGB, hex-code, and color-names as of now. However, you can get CSS variable value in JavaScript using getComputedStyle() as shown in the code snippet below.
function getCSSVarValue(name) {
return getComputedStyle(document.getElementById('chartContainer')).getPropertyValue(name);
}
Please check this JSFiddle for a working example.
__
Rohith Nagaral
Team CanvasJS