Hi There,
What you need is a good sized round aiming mark that you can make a lollipop sighting picture with at 100 yards. The normal black targets are good for this as you can sit it on top of your foresight with a minimal white gap between the sight and aiming mark this is to stop you firesight merging with the aiming mark. Bright colours like Orange whilst making it easier to see the bullet holes do not actually make good aiming marks as they tend to fuzz out and not remain sharp and clear in definition to the eye.
NRA 100 yard small bore targets are probably a good bet. Good luck and let us know how you got on.
Edit:-
Whoops didn't proof read and was horrified at the spelling mistakes and mistypes