Created by generating a conical 'Full Saturation spectrum CW' gradient in GIMP in a 400x400 image (from point 200,200 to 200,399), scaling to 200x200 (bicubic resampling), importing PNG into Inkscape <b>as an <a href="//commons.wikimedia.org/wiki/Category:SVG_images_with_embedded_raster_graphics" title="Category:SVG images with embedded raster graphics">embedded raster graphic</a></b>, gaussian blurring (SD=5), then masking to two XORed circles.
<a href="//commons.wikimedia.org/wiki/User:Gringer" title="User:Gringer">Gringer</a>
<span class="int-own-work" lang="en">Own work</span>