Fix invisible prompt color on dark terminal background

[Ravenlol119]

Description

This Pull Request modified the InputReader class, it fixes #6190.

Before: Gray Prompt , it has Low Visibility on Dark Backgrounds, or maybe invisible on some dark themes.

Now: Bright Cyan Prompt, Improved Visibility, it can be seen clearly on both dark theme and bright theme.

Release notes

The prompt is now displayed in bright cyan, making it more readable on dark backgrounds.

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[ebyhr]

Could you add the screenshot before&after this change to the PR description?

[Ravenlol119]

Sure

[ebyhr]

Thanks for attaching the screenshot!

I can see the prompt though the PR title is "invisible". I feel there is no need to make it stands out because it is just a prompt which is not so important. I would leave the review to @wendigo who create the issue #6190.