The speed of light is a constant, the distance it has to travel is what causes the shift in color, not whether it is speeding up or slowing down.
Here's a little experiment for you to try.
Have a friend stand at the end of the block while you are on the other end.
Have them say in a clear normal voice "I am Standing here" repeatedly.
Start walking towards them. As you get closer you begin to kind of hear them, but not distinctly until you are much closer.
This is an example of the Red shift in the Doppler spectrum indicating closer distance the light has to travel.
Now, start walking away from them until you cannot hear what they are saying.
This is an example of the blue shift in the Doppler changes. The volume has not changed, but the distance it has to travel has.
No, the speed of light is not constant. I know it’s beyond your grasp, so I won’t bother explaining.
Gezz, even Newton knew that.