How do you sample colors / or use a color palette? can you do this on medibang paint?
You can use the Eyedropper tool on the main toolbar (shortcut key: I, for a verbal pun - thanks for the reminder, queenlinee!),
or hold the Alt key (Windows) to temporarily change the current tool to the Eyedropper (Macs the same, anyone?), changing back to the current tool when you release,
or you can use right-click (mouse or pen side button) for Eyedropper colour sampling (File menu, Environment Setting to change right-click from Eyedropper to Eraser.)
You can use the Window menu, Palette to display the Palette window. Use the icons at the bottom of the Palette window to add the current colour or another colour to the palette. Click on a palette colour to change the current colour to the palette colour.
Note: you can also load an image in the Reference window (Window menu, Reference) and set the Eyedropper tool above the reference image while still using the Brush tool on the main canvas. That way you can click on the Reference window to choose a colour, then paint with that colour on the canvas.