Rainbow Spectrum Gradient

A full spectrum blends smoothly from red through orange, yellow, green and blue to violet across the frame.

Work along the spectrum in order, but do not rely on hue alone. Brightness changes as well as color, particularly around green, blue and violet. The puzzle becomes difficult where adjacent shades are close, so arrange small runs on a flat line before joining them into the full sweep. For a harder board, use rainbow spectrum gradient as the centre of a few short runs instead of searching for one large match.