fix(curve):color_map_z setting works + general color validators

Description

Due to typos in color_map_z kwargs the colormap gradient for 2D z scatter was never respected and felt always to 'plasma' colormap, which is default.

Reusable color validators for colormaps in current instance and checking colors against correct HEX format, RGBA or CSS colors.

Related Issues

closes #210 (closed) #127 (closed)

Type of Change

• color_map_z is now respected
• color_map_z is checked with pydantic also after creation with model_config: dict = {"validate_assignment": True}
• utils.Colors general colors and colormap validators

Definition of Done

• Documentation is up-to-date.
• add tests