How much attention do you want on the spring/shock? If you have too many "Pops" nothing pops and it looks like the farkle fairy cursed your bike. If you know the color scheme for the tank and any painted bits you need to think through the way the colors will be seen as you look at the bike. A bright yellow spring might not go so well if you were going to paint the bike a bright purple with lavender pinstriping...
Yeah, I know...extreme example...but there are people who would like something like that. I don't want to know them, but they are out there.
What is the body of the shock going to look like? The clevises or ends of the shock are going to be silver/chrome/black?
You don't want the spring to compete with the flow of the lines you create. The subtle things you find when looking at a bike tend to be rich to the senses and eyes as you look closer. It will be lost on some, but those with a discerning eye will find new things many times when looking at the bike. It is not that they are buried or understated too much but they are well integrated and contribute to the overall look and feel of the design elements you choose.
That's my take...
Yellow shock, yellow plug wires, yellow pinstripe on the wheels?
If yellow is one of the themes it might work...
Sulfur Yellow and Chrome and Silver go together very well and with the right amount of excellent chrome or polished parts it can be a stunning bike...just don't overdo the amount of yellow on the bike...not all can pull it off.
David