After the last Material Theme update (v.5.2.2), in Rubymine the Tab Bar is a bright color (see screenshot). It displays properly in Webstorm.

You probably activated inadvertently the "Accent Mode" feature. You can disable it via the settings.
Thank you that was it. There are so many settings in MT they are hard to find sometimes. Thanks for a great fast evolving product.
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You probably activated inadvertently the "Accent Mode" feature. You can disable it via the settings.