Good question.

The test will never come back perfectly clear. It will only change from dark pink to light pink.

If you watched the video, there will be a control cell from a bitch's plasma that is NOT in estrus, as well as from one that IS in estrus.

Use those control test cells to compare to your bitch

If your bitch's result is darker, like the cell where the bitch isn't ready, then your bitch isn't ready either;
If your bitch's result is as light (or lighter) than the control where the bitch IS ready, then your bitch is ready too.

That is why they give you a sample of in-heat plasma, as a control, as well as one not in heat, is so you can see which cell your bitch's test cell looks like most

Good luck,

Jack