Next question I have with camera is: is the camera.x, .y,.z an absolute coordinate independent from pan, tilt and roll?
I used: vec_set(camera.x, vector (-40, 20,30));
and found out a strange behaviour. ths axis are twistet.
-40 equals .z, 20 equals .y, and 30 equals .x
The same is with the colour vector which I changed in the atype.h that red is always the first colour vector. Why is this? Every graphical program I know has red as the first vector.

color-vectors are BGR (has something to do with the communication between acknex and direct-x), so if you use
vec_set(sky_color.blue, vector(200, 100, 0));
it is R=0, G=100, B=200.

However, the camera-position is absolute and independent from pan tilt and roll but x, y and z are not swaped.
If pan, tilt and roll is 0 the camera is looking in the direction of the x-axis.

So: X is forward, Y is to the left and Z is up.

Is this coordinate system hardcoded or is there a way to switch to the directx left handed cartesian system like it is used usually in directx?

Thanks for answers.

The coordinate system of 3DGS is fixed, you cannot change it.

Just think of all the overhead that would arise from providing different coordinate systems...