Leather can be worked well, but needs practice. If the nick has left a hollow, you can use leather filler, and then recolour the area, and apply a varnish, which must be mixed to get the right balance of shine or silk finish.
If this is in a high vis area, you could make it worse. I've done this three times successfully, but on black leather. The first was a badly worn patch on the seat backrest, which recoloured and varnished invisibly. The second was a sticky patch on the inner sill cover. In the end I had to sand this down using white spirit, and fine emery paper, then recolour & varnish to match. The third was more serious where a damaged rivet on my jeans put a sawtooth groove in the seat backrest. That took filler, sanding recolour and varnish to get right. Black is very forgiving. Colours not so easy.
https://www.furnitureclinic.co.uk/leather-care-products/leather-repair
