You're right that the end grain of a toothpick or plug will show up as a round black circle in the wood.
If you seal the end of the plug first with some superglue or something similar, the end grain won't color much, if at all. If you want to go that route, note what the final color of the stock wood will be where the plug is going.
No matter what, don't expect a piece of Chinese toothpick wood to perfectly match your piece of maple.
The Best choice would be a piece of you stock wood, fitted to the hole with correct grain orientation.
John