Quoting someonesangel:" Your urine was more diluted with the lighter one. Drinking a lot of water and urinating frequently can ... [snip!] ... time to build up. Thats why they say its best to test with morning urine. Light or dark, a positive is a positive. Congrats!"
Quoting SAFFY™:" Never test in the morning. Test in the late afternoon or early evening. I preferred to test around 3pm ... [snip!] ... To be perfectly honest, I hate OPKs. I had more success with the fertility monitor but I borrowed it from a friend. "