Stats: Use correct color for visitors

[nbradbury]

Fixes #21366

As noted in the issue, in dark mode stats didn't differentiate between views & visitors, instead showing them in the same color. This PR addresses this.

To test, simply verify that views and visitors are shown with different colors in both dark and light modes. Before and after shot below.

[dangermattic]

	1 Warning
:warning:	PR is not assigned to a milestone.

Generated by :no_entry_sign: Danger

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr21476-c4ae15f
	Commit	c4ae15f3e6d6237d923b7ab0934799db70eb0b08
	Direct Download	jetpack-prototype-build-pr21476-c4ae15f.apk

Note: Google Login is not supported on these builds.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr21476-c4ae15f
	Commit	c4ae15f3e6d6237d923b7ab0934799db70eb0b08
	Direct Download	wordpress-prototype-build-pr21476-c4ae15f.apk

Note: Google Login is not supported on these builds.