I would say based on. Haiku is inspired by BeOS R5, not based on it. Not your wording, I know.

GTK2, Balou & mouse cursor themes included to "BEOS-inspired-theme " are inspired by the simple, intuitive and clean apperance of BeOS GUI.

Even, if our WM's are look-like R5, they are created from scratch and according to R5 - they are different in apperance.
They are more complicated 8)

"BEOS-inspired-theme " is not a copy of BeOS theme.
Each of the images used there was a hand-created from scratch, and they are not using any of oryginal BeOS images.
None of the lines of code used in configuration files of these themes does not come from the BeOS operating system. They are not using any of BeOS code.

Haiku operating system (since it's foundation) is created with the assumption of binary compatibility with oryginal BeOS system - also with compability of BeOS R5 native file system (BFS), so here we can say that "Haiku is based on BeOS". Can we say that? I think, we can. Native programs (bearing in mind the GCC compatibility) designed for BeOS can run on Haiku without problems, little faster maybe...

Those themes presented above are not copies of BeOS GUI or copies of BeOS code, so they are not based on it (ZETA is based on BeOS).
They are only inspired by (great not only for me) BeOS GUI, and they are clearly different than few WM's available for Linux GUI for years (for example - Xfce4' B5)

If someone create new theme with wood elements inside (wood pictures in background), then can we say: "That theme is wood based"?
No, it's only inspired by clean, worm & natural wood apperance. That's all.

:-)

First, my comment was just about the window decorations -- IceWM theme.

I use the same wording "BeOS inspired" in describing my pekwm theme, which means (I like to think) that it's not look-like. This is my point.

I do not question the effort in creating the "BEOS-inspired-theme" pack, or that it is right doing.

I have to admit that the titlebar buttons are more different at the pixel level than I first thought. But I still think they're "based on" BeOS, even if they're not copied, and even if you could restrain yourself from zooming in a screenshot and picking colours of pixels. At least, you have a very clear idea of how these buttons look at the pixel level and base your drawing on that. Drawing quite identical buttons from scratch is easier than finding the original images.

Writing thousands of lines of code in Haiku is not based on the actual thing being recreated.

About windows decorations i can agree with you, but gtk theme is realy inspired by beos-r5.