Yup its Sun Up, Sight up, Sun down Sight down. Also applies to windage.
When its bright, the sight has a tendency to bleed into the target, the bull appears smaller. Then when a cloud passes over the bull looks bigger and one tends to shoot lower. The same for the sun coming from the left or right. If you're shooting north, in the morning the sun will shine from the right (east) so the same applies, you click into the sun. Later in the afternoon the sun comes from the left or west, you click the other way.
I've found shooting 308s for over 35 years I need to click on MOA into the sun. Some people may be different, some may click less, some may click more.
The most important part is to record the light conditions in your score book. HP score books have a spot for recording light conditions. Simply point the top of the book to the target, hold your pencil straight up and look at the shadow. Draw an arrow indicating the light direction. It doesn't take many matches to see how light affects you.
Me I know my zero and its set on bright sunlight, I take that into account with I fire my first shot. If its sunny, I go with my zero, if its cloudy, I click down. My windage zero was obtained about noon, so if I start shooting in the morning, (assuming I'm facing north) I click right or into the sun.
But I mark my changes, and indicate why, indicating if its the light that caused the change. I make the wind adjustments from there.
Again the most important part is to RECORD it. Record everything, and indicate why you made any changes you made.
If you make a change for the light, you don't want to confuse it with your wind changes.