Highlight a region in an image if user touches it

for example we have an image with 4 regions. It is a still image (UIImage).

The image background is transparent and the regions are marked out with the black color. The regions have different forms, colours and positions.

if user touches the region 2 - it is highlighted, if user touches the region 4 - it is also highlighted.

I want to detect if user touches a region and then highlight it inside with its own colour.

Can someone please explain how can I achieve this in swift?