You can't add the separation line like you ask, certainly, not in playing now view anyway. In other views, you could potentially skin it in, by way of editing the 'Grouping' separator, and then setting the grouping how you want it, which is typically via hard coded clever defaults, or any available library field, where of course, you are free to create any field you want and so manipulate how your lists are grouped. It's very powerful, but maybe a bit overkill for what you want.
As for the colouring...
There's a lot of work if want the whole row coloured, more than is sensible to be honest, so, you're options are...
Create the expression based around a single field, and settle for that. How?
Right click a column header and choose "Add expression column". Name it in the top field. Here, I've used the [Genre] field as an example... Below name, enter your expression. "IfElse" is neat, here's why... The expression first...
ifelse(isequal([genre],Blues),<font color="0x0e02fe">[genre]<//font>,isequal([genre],Rock),<font color="0xfe02c0">[genre]<//font>,1,[genre])
This says, if genre=Blues, then use blue text, if genre=Rock, then use pink text, otherwise, just show the genre. The beauty here is that you can just keep adding these in before the "1,[genre]" at the end, and it will keep working. So, inserting "isequal([genre],Ballad),<font color="0x000000">[genre]<//font>," would turn all Ballads white, and so on... You could also create a library field using the same expression to make it easier to add to any view you liked.
If you want the whole line coloured up, you could get that by cheating. You would create either an expression based field or column that included all of the fields you wanted to see columns for, [artist] - [album] - [name] - Played [number plays] times - Last Played on [last played], for example, and then build the expression to colour keying off that new field instead of [Genre]. The two issues here you might not be able to live with are, that you would have to forego inline editing, and the pseudo columns won't line up nicely. You would be strictly reading from left to right.
The only other way is to create colouring expression columns for the whole view, so, still keying off the genre field, the two expressions below would give coloured Artist and Album fields depending on the genre.
ifelse(isequal([genre],Blues),<font color="0x0e02fe">[album]<//font>,isequal([genre],Rock),<font color="0xfe02c0">[album]<//font>,1,[album])
ifelse(isequal([genre],Blues),<font color="0x0e02fe">[artist]<//font>,isequal([genre],Rock),<font color="0xfe02c0">[artist]<//font>,1,[artist])
You would have the full line, but again, no inline editing.
-marko