function restoreContext() {
      curContext.restore();
      isStrokeDirty = true;
      isFillDirty = true;
    }
Blends two color values together based on the blending mode given as the MODE parameter.
The possible modes are described in the reference for the blend() function.

@param {color} c1 color: the first color to blend
@param {color} c2 color: the second color to blend
@param {MODE} MODE Either BLEND, ADD, SUBTRACT, DARKEST, LIGHTEST, DIFFERENCE, EXCLUSION, MULTIPLY,
SCREEN, OVERLAY, HARD_LIGHT, SOFT_LIGHT, DODGE, or BURN

@returns {float} The blended color.

@see blend
@see color