Implement color themes

[Valentin-v-Todorov]

• Add predefined color themes (dark, light, high-contrast)
• Allow custom color configuration for priorities, tags
• Support NO_COLOR environment variable

[agoritma]

Hi @Valentin-v-Todorov
i willing to work this feature under Hacktoberfest, can you assign it to me?

[Valentin-v-Todorov]

Thanks for the contribution @agoritma ! Don't forget to link your PR to the issue ✌️