JMC 7 UI displays hints/tooltips with invisible text (black font on black bckgr)

ADDITIONAL SYSTEM INFORMATION :
recent KDE Plasma 5 on updated Debian Sid and Arch (both 64bit), JRE shipped with JMC

A DESCRIPTION OF THE PROBLEM :
While moving mouse over any element of recording, presented hints/tooltips display black font on black background - so they are invisible. Lack of hints/tooltips make JMC almost useless.
The problem is observed in JMC 7 (all builds until now), but it didn't exist in JMC 6 (tooltips/hints were presented in white font on black background).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :

• start newest build of JMC 7
• load any flight recording (can be the one from JMC itself)
• click on "Java Application" in Outline (left panel)
• move mouse over chart visible in the main section

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Info in tooltip/hint is visible (like in JMC 6)
ACTUAL -
Info in tooltip/hint is rendered as black font on black background - so it's invisible.

FREQUENCY : always