This completely desaturates (turns greyscale) parts of the image that match the selected color.
This tool offers both freehand and one-click operation.
This tool offers multiple size settings.
See also: 「いろのこし」, 「ほうわ」, 「ひほうわ」, Darken, Lighten, Tint, & 「だっしょく」.
Tux Paint 0.9.31