Would it be possible to take the national/EU transport authorities to court to complain about risking lives and discrimination? Am I missing something?
Transport authorities are not responsible for the design of traffic signs. The designs are part of traffic laws, typically based on the Vienna Convention for Road Signs and Signals. To force a change to the designs, other than lobbying for changes directly, there would be a legal challenge on the grounds that these designs are unconstitutional to a degree that outweighs the benefits of uniform signage across countries, or other legitimate reasons in favour of the status quo.
This will be difficult, as traffic signs already convey their information in redundant manner, combining both overall shape, high-contrast symbols, and the colours itself. Thus, even a colour-blind person is able to read the signs.
Your argument is slightly different, that colour blindness makes it more difficult to spot the signs. This ability varies from person to person, but even people with normal vision can have difficulty spotting and understanding signs, regardless of their colour (or even because a color!). Here, there might be another opportunity for a legal attack: that signs have been mounted to close to each other or that they aren't visible enough due to their surroundings. But simpler sign locations would benefit all traffic participants, so I don't think focusing on the colour-blind angle would provide additional weight.
In any case, the status quo is: if you are unable to safely see traffic signs, you are unfit to drive. It is reckless to drive in a manner that prevents you from reading signage, e.g. if you are driving too fast. This is not necessarily an illegal form of discrimination.