Correct.
It's not the price differential you need to worry about, it's the ability to be able to even find a buyer full stop.
I agree, the GT is not that great in reality, especially compared to aftermarket equivalents, but it what buyers want.
A car is only worth what someone will pay for it. If the colour is rare or desireable then they will be prepared to pay more for it.
Search PH for Ferrari 360's.The first 15 or so are usually Silver. The decent colours (Nero,Rosso,TDF & Giallo) are priced higher as they are more desireable.
Colour makes a huge difference on price. Fact.
As for not buying a car because it's going to depreciate.....
As a seller I wouldn't accept more than about a grand in cash.
And as a buyer i wouldn't walk around with a load of cash on me.
Safest option for all concerned is to take/pay a small deposit and then meet the buyer/seller at their/your bank with either a Bankers Draft or the cash so the Bank can confirm authenticity.
Also, don't pay anything with a written receipt stating the amount payable in total, whats it's for and dated and signed by both parties.