Card Game Trouble

Hello, I'm new at game devoloping and I started to make a card game. I have 25 image-based slots in a one panel. I achieved to drag card images to these slots with importing IDraghandler and lock them when dragging is finished.

What I want to do is, when I clicked to placed a card, I want to change it parent's (slot's) background color. Also I achieved it for just one slot, but i want to make it for another slots where are on up-down-left or right of clicked slot by dragging. If I continue holding mouse button or touching on phone's screen, and drag to another card that placed on slot, I want it's background color is changed.

Actually, in short, I want to listen from clicking or touching to lifting. I'm looking tutorials but i couldn't find it and waiting for your advices, Thank you