Pick new color theme for F3D

[mwestphal]

In the context of #845, we realised now it the right theme to pick a new color theme for F3D, let pick it together!

[mwestphal]

Here is the first pick of colors suggested by @mariami:

[Meakk]

For reference, there's a tool from Adobe allowing to create palettes: https://color.adobe.com/create/color-wheel

Here's a "compound" palette of 4 pastel colors I just created:

[MarieZedginidze]

We have these shades of blue and yellow for the links and CTA buttons for now:

[MarieZedginidze]

I picked different shades for all four colours. The light version of the UI will have light grey for the background instead of white:

Figma file is changed too:
https://www.figma.com/design/kIfYeOwdTw5DBylCn07ZXN/F3D-Design?node-id=346-8&t=gdy2YS2EJf5jyjjA-1

[mwestphal]

The last proposition by @MarieZedginidze has been picked! Thanks a lot!

[Meakk]

Should we also use the new colors for the app itself? e.g. new background color:

current:

new (#141414):

[mwestphal]

Isnt it a bit too dark for a background ? color theme doesnt really matter in that case imo.