Fixes #4614: Changed the background color according to accessibility scanner.

[suyashshenoi]

Fixed: Topic Images to match A11YS

Explanation

Essential Checklist

• [x] The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• [x] Any changes to scripts/assets files have their rationale included in the PR explanation.
• [x] The PR follows the style guide.
• [x] The PR does not contain any unnecessary code changes from Android Studio (reference).
• [x] The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• [x] The PR is assigned to the appropriate reviewers (reference).

The topic and recently played images no longer have an issue with the Accessibility Checker.

This is a fix. Resolves https://github.com/oppia/oppia-android/issues/4614

[adhiamboperes]

Thanks @suyashshenoi! Could you please also add the updated screenshots for the "Recently Played Stories"?

[suyashshenoi]

@adhiamboperes I have added the updated screenshots for the "Recently Played Stories" too. Pls check it and let me know if anything else is remaining. Thank you.

[suyashshenoi]

@BenHenning @adhiamboperes PTAL.

[oppiabot[bot]]

Unassigning @suyashshenoi since a re-review was requested. @suyashshenoi, please make sure you have addressed all review comments. Thanks!

[oppiabot[bot]]

Unassigning @BenHenning since they have already approved the PR.

[oppiabot[bot]]

Hi @suyashshenoi, this PR is ready to be merged. Please address any remaining comments prior to merging, and feel free to ask someone to merge your PR once the CI checks pass and you're happy with it. Thanks!