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Photography & graphic design
3D
32x32 Free Design Icons
yes, mark, Apply
Black
32x32
Signs & symbols
Free 3d Glossy Interface Icon Set
yes, mark, validation
64x64
UI
Gnome Web Icons
Apply, Dialog
DarkOliveGreen
Dialog, 48, tick
48x48
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yes, ok, tick
Desktop apps
Illumine
Things, Apply
LightGray
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Free Applications Icons
ok, success, Accept
24x24
red, tick, yes
Check, Accept, green
Glaze
Blue, Apply, Check
CornflowerBlue