My IC's have slowly gotten darker. I'm 13DPO right now and I'd say the line is half as dark as the control. However, I've noticed that the morning one is lighter than the afternoon one I take (I've got a ton laying around so I'm poas all the time haha) This chart really helped me to understand hcg doubling times more clearly. Yes most of us know when we ovulated.....but you cannot really say with accuracy when you implanted and this chart gives HCG estimates based on both showing how even if you ovulated a certain day, your levels could rise "slowly" based on the date you actually implanted.
https://whenmybaby.com/implantation-doubling-calculator.php
I scoured the internet looking at other's examples of their line progression using IC's and MANY if not ALL of them were VERY slow to show a solid line and most didn't get as dark as the control line until between 20-30DPO!! I'd relax a bit with judging the line darkness. Have you had your pregnancy confirmed via a blood test through your Dr? That would help you to know the certainty of your HCG progression (as long as you get a 2nd blood test two days later to check for HCG doubling)