Allows setting/resetting `entity.rgb` to `None`

[kkkkkom]

Hi, @mozman , could you please review this minor merge request?

I think we should allow entity.rgb to be set/reset to None.

Many entity rgbs are initially None by default, and this change will allow users/developers to temporarily set rgb and reset it back without causing an error.

pytest has passed clean locally.

[kkkkkom]

This is not the correct way.

If you rally need this feature implement the @rgb.deleter method and check if the attrib true_color exists otherwise a DXFAttributeError will be raised.

Thanks for reviewing, I'll update accordingly

[kkkkkom]

Hi, @mozman , could you please review again?

[mozman]

@kkkkkom thanks for the idea, to speed up the process I added all the necessary changes myself

[kkkkkom]

@kkkkkom thanks for the idea, to speed up the process I added all the necessary changes myself

Thanks!