I wanted to add an custom icon for _Peek_, a screen casting tool for Ubuntu. Instead of troubling you, I thought I would make one and drop Peek.svg ( inkscape svg ) to 16, 22, 24, 32 and 64 folders.
But, strangely, it does not work at all. I get the old icon for the app. What to do ?

v2

Do you want to add the icon to your own icon theme, or you want to make a pull request?
@SmartFinn , I have copied Papirus folder into .icons under Home where I do my customizations. I wanted to replace Peek's default icon. So it can be called _my own icon theme_
The issue is, even after adding all those SVGs to corresponding folder, the default icon is not replaced. Kindly advise.
Icons name should be:
Filenames must be lowercase.
@SmartFinn
com.uploadedlobster.peek.svg
I added this in usr > share >applications > Peek.desktop
in it, Icon=com.uploadedlobster.peek.svg
and renamed all Peek.svg to peek.svg in the folders. But I still get the default icon. Any help possible ?
Create symlinks in each folder:
ln -sf peek.svg com.uploadedlobster.peek.svg
or rename peek.svg to com.uploadedlobster.peek.svg
What are Symlinks ? How does it help ?
ln -sf peek.svg com.uploadedlobster.peek.svg
In which folder should I run this command from ? Thanks.
Can you share the general format of changes to be adding while including a new icon ? What goes where ?
I managed to solve the issue on adding icon to Papirus. Just that, one version( 48x48) comes like this when searched on dash. I see the same on icon preview on apps folder ( 48x48). But no black when I open it with Inkscape.

Can you share the general format of changes to be adding while including a new icon ? What goes where ?
https://github.com/PapirusDevelopmentTeam/papirus-icon-theme/blob/master/tools/work/README.md
Just that, one version( 48x48) comes like this when searched on dash. I see the same on icon preview on apps folder ( 48x48). But no black when I open it with Inkscape.
The icon doesn't relate to Papirus icon theme. I can't help you.