Softimage XSI
Community-made theme, based on the Softimage XSI UI.
There are three versions, the theme that came with Blender up till version 4.2.x, one adjusted theme for version 4.5.x and one adjusted theme for version 5.0 and up. Choose the right one for your Blender version.
For an even more aligned 'Softimage' experience, have a look at the 'K-Tools Mode Highlight' addon as well.
What's New
5.0.0 December 17th, 2025
v.5.0.0 - Theme adjusted for the theme changes in Blender v.5.0.x For Blender 4.2.x or 4.5.x download the appropriate theme.
A very good factually white theme (Blender Light is Not light enough for me) that simultaneously is easy on the eyes. The only gimmick is that text on the status bar is barely visible against the background. You can mitigate that by going into Preferences>Themes>User Interface>State and changing the first four to be of a less dark, and possibly less saturated colour
This version of the theme for v5 is broken in several areas, especially in the asset shelf. I uploaded a tweaked version for download here: https://projects.blender.org/extensions/theme_xsi/issues/3 Hopefully the mods can switch them out, so the theme works properly again :)