I had some betas done a few months before this pregnancy and I picked up a bfp on frers with a hcg at 6. On that footing, it would have taken me 6 more days of doubling to proc a positive on a CB digi! If you catch a bfp early, which you have, it can take a bit of time chick. Im sure youll get your positive on a digi soon!
As for ICs, I found they never got very dark for me. Some brands just dont..this might be the darkest they will get. Defo still positive tests tho! x