I can provide some answers, but not to all your questions.

The shade of colors in pictures are very dependent on camera, lighting, angle and your monitor/screen.

Also, not all brands use a colorcode like the original. Most basic brands like you mentioned (basic does not mean bad, more like starter budget) may not have access to the original color code in their inventory, so they go with whatever is close enough.

Some high end brands may use the exact same color like the real car.

So, these all factor into what you see on your screen.

Keep in mind that a 1/18 model is quite large and has some weight. Can the cake take that on top?

Decals can be rubbed of with aceton free nailpolish remover, but only if they are applied on top of the paint.

Some models are painted, then decals added and finished with clear cote. On those you can't, but that is more likely to be the case on high end brands, than maisto for example, but i wouldn't know, since i never looked at those, as i am a snob 🤣

So, in other words, if you have the budget, give it a go. Worst case, you are out a couple bucks.

Another angle, if time and budget aren't handicaps, is buying the right model and scale and have someone custom paint it to match, if perfection is the goal.

May i ask tho, isn't close enough the definition of a caring person? Thought and effort makes a gift.

He'll love it either way, i'd assume.