Hey there!
For finding the top of the latest response right now: in the Agents window you can jump between your own messages. On Windows, Ctrl+Shift+U jumps up to your previous message and Ctrl+Shift+Y to the next. Landing on your last prompt drops you right where the latest response begins, so you can read it from the top. These aren’t in the command palette, so they’re easy to miss.
On the contrast itself: in the Agents window the message background follows your editor theme, so it ends up quite subtle, and there isn’t a setting to boost it today. Stronger visual distinction for user messages is recurring feedback we’re collecting, and you can add your vote here: Highlight user-authored messages in chat threads. A dedicated “jump to the start of the latest response” button has also been requested here: Scroll to start of answer.
Give the shortcut a try and let me know if it helps in the meantime!