Sakai Jewel logo and background do not pass color contrast check

The new jewel logo added in SAK-39935 doesn't pass Webaim's accessibility contrast check. The jewel part has a fg color #68A9DD with bg #414CA6 and fails The old logo looks like it was a little lighter. I'm okay with changing up the background for 13 too!

Since we're being big on accessibility I feel like this should new stay in 13 until we either have a different color for the logo or different color for the default background of Sakai that passes.

[1] https://webaim.org/resources/contrastchecker/