A darker and lighter color on the test paper may be due to a short period of pregnancy, abnormal embryo development, failure of the test paper, or incorrect testing method. 1. Short pregnancy time: the test paper test is to test the human chorionic gonadotropin (HCG) in the urine to show a double bar, when the pregnancy time is relatively short, the HCG concentration in the urine is low to form a weak positive. 2. Abnormal embryonic development after pregnancy: After pregnancy due to abnormal embryonic development, ectopic pregnancy, etc., resulting in low levels of HCG in the body, which can be manifested in the phenomenon of test strips with one deep and one shallow. 3. Test paper failure, test method is not correct: test paper expired, or manufacturers of quality problems, or test method is not correct, may produce weak positive. The test paper on a dark and a light, you need to go to the hospital in time to take a blood test HCG to confirm whether the pregnancy, but also need to rule out ectopic pregnancy and other cases, if you need to promptly seek medical treatment.