The Color String option can prove to be a real time saver if used correctly. Since the object of the game is to get 1 thru 9 on each color as it is with each side, your attention must constantly be on these color strings. Vollying back and forth between the cube (in either 3D or 2D mode) and the color strings can prove to be time saving.
In the example below, two sides of the cube have been completed (Diagram 1). A quick visit to the Color Strings (Diagrams 2 thru 7) shows us two of the color strings have been taken to the point of only one remaining number. These are Quick Hits (Diagrams 3 & 6).
Color String are another good way to check the veracity of your puzzle to make sure you do not have any duplicates on a color string that you may not have seen on opposing sides of the cube.This can only happen if Auto Corrector is off, which is the option of choice for those wanting a more challenging experience.
Keep those colors in tact. Use the Color Grid icon with frequency and you will see your puzzle times go down.