Streak marks in plaster
Getting some streak marks when troweling up is the plaster too wet at this part or to dry maybe?
It looks like it could be due to a lack of pressure, as the trowel is only making contact with the highs. Where it makes contact it changes colour so the colour shading is showing where the hollows are.
How to rectify
When the plaster is still pliable it is important to push firmly, and if the trowel is at the correct angle (leading edge approx 10 - 20mm away from surface) the highs will be pushed into the lows. But you do have to push hard. If plaster collects on your trowel then it is scraping it off the highs but not flat enough to push it into the lows, so just flatten your trowel into the wall and all should be good. The firmer the plaster is the harder you'll have to push.