How to reduce cracking and increase browning in sourdough loaves?
For the scoring, you didn't score deep enough. You need a lot more depth to allow for enough expansion. 

For the browning, you cannot expect much from a sourdough in a home oven. Both the ingredients and the temperature are wrong for a dark crust. The best you can do is to work with washes, milk should brown well, yolk is also OK but not as usual on sourdough.