some programs like gparted don’t necessarily get their icons (depending on the theme i think) from the theme. if you look at the properties for the gparted package in synaptic package manager (or you can run dpkg -L gparted), you might see something similar to this under the “installed files” tab:
most of what you see about a program on your desktop or menus comes from a .desktop file in /usr/share/applications. the beginning of my gparted.desktop file looks like this:
so for my theme and system, that icon is souced from the above list depending on the size i have chosen for my icons.
if you aren’t seeing an icon, you can replace that line with an absolute path (for example Icon=/usr/share/icons/hicolor/48x48/apps/gparted.png) to an icon of your choosing if you do have the stock gparted icons. or you can search the icons in your preferred theme to see if there is one you prefer. most icons on ubuntu-based systems are installed to /usr/share/icons, but there may also be also some in ~/.icons or possibly even ~/.local/share/icons.
Thank you for answering, but what I meant was that the icons are missing inside of the applications. Take Synaptic for example - no icons on the buttons. GParted does not have them either.