PhotoPlus X6 User Guide - Serif

Gradient Fill Tool
Painting, Drawing, and Text 137
Whereas solid fills use a single colour, all gradient fills in PhotoPlus utilize at
least two "key" colours, with a spread of hues in between each key colour,
creating a "spectrum" effect. You can fine-tune the actual spread of colour
between pairs of key colours. Likewise, a gradient fill in PhotoPlus can have
either solid transparency—one level of opacity, like 50% or 100%, across its
entire range—or variable transparency, with at least two "key" opacity levels and
a spread of values in between. (Remember that opacity is simply an inverse way
of expressing transparency.)
The Gradient Fill Tool lets you apply variable colour and/or transparency
fills directly to a layer.
Solid Linear Radial
Conical Square