lisp: use more legible colors on dark backgrounds
lisp: use more legible colors on dark backgrounds

On dark backgrounds, the color for the current transaction makes the
text quite unreadable. Let's use a darker color in this case. Maybe some
other colors could be adjusted.

duncanmortimer/ledger,jwakely/ledger,paulbdavis/ledger,jwakely/ledger,ledger/ledger,paulbdavis/ledger,duncanmortimer/ledger,duncanmortimer/ledger,ledger/ledger,afh/ledger,duncanmortimer/ledger,ledger/ledger,afh/ledger,paulbdavis/ledger,jwakely/ledger,jwakely/ledger,duncanmortimer/ledger,paulbdavis/ledger,paulbdavis/ledger,jwakely/ledger,jwakely/ledger,duncanmortimer/ledger,paulbdavis/ledger,jwakely/ledger,ledger/ledger,afh/ledger,afh/ledger,paulbdavis/ledger,ledger/ledger,duncanmortimer/ledger,afh/ledger