Install this package:
emerge -a x11-themes/mate-icon-theme
If the package is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask
emerge
autounmask x11-themes/mate-icon-theme
Or alternatively:
emerge --autounmask-write -a x11-themes/mate-icon-theme
<pkgmetadata> <maintainer type="person" proxied="yes"> <email>immoloism@gmail.com</email> <name>Ian Jordan</name> </maintainer> <maintainer type="project" proxied="proxy"> <email>proxy-maint@gentoo.org</email> <name>Proxy Maintainers</name> </maintainer> <upstream> <remote-id type="github">mate-desktop/mate-icon-theme</remote-id> </upstream> </pkgmetadata>