Table cell background colors are lost in Email notifications

Problem

A Confluence page contains a table with colored cell background. The colors are lost in email notifications.

Environment

Confluence 7.5.2 with SMTP Server configured.

Steps to Reproduce

1. Have 2 users configured admin and user1 in Confluence
2. Create a Mail Server in Confluence (for instance using Apache James) and configure a mailbox for user1 email address
3. Watch a space for content creation and update with user1 (to trigger email notification)
4. Create a new page in the space with admin user:
   • Storage format can look like below

     <p class="auto-cursor-target"><br /></p>
     <table class="wrapped"><colgroup><col /><col /><col /></colgroup>
     <tbody>
     <tr>
     <th class="highlight-#bf2600" title="Background colour : Dark red 100%" data-highlight-colour="#bf2600"><br /></th>
     <th><br /></th>
     <th class="highlight-#000000" title="Background colour : Black 100%" data-highlight-colour="#000000"><br /></th></tr>
     <tr>
     <td class="highlight-#36b37e" title="Background colour : Medium green 100%" data-highlight-colour="#36b37e"><br /></td>
     <td><br /></td>
     <td class="highlight-#6554c0" title="Background colour : Medium purple 100%" data-highlight-colour="#6554c0"><br /></td></tr>
     <tr>
     <td><br /></td>
     <td class="highlight-#79e2f2" title="Background colour : Medium teal 45%" data-highlight-colour="#79e2f2"><br /></td>
     <td class="highlight-#fff0b3" title="Background colour : Light yellow 100%" data-highlight-colour="#fff0b3"><br /></td></tr>
     <tr>
     <td class="highlight-#ffebe6" title="Background colour : Light red 35%" data-highlight-colour="#ffebe6"><br /></td>
     <td><br /></td>
     <td class="highlight-#eae6ff" title="Background colour : Light purple 35%" data-highlight-colour="#eae6ff"><br /></td></tr></tbody></table>
     <p class="auto-cursor-target"><br /></p>

5. Monitor user1 mailbox for email notification and confirm the issue

Expected Results

user1 should receive an email notification with colored background cells for the Table.

Actual Results

Table cell background colors are lost in email notifications.

Workaround

N/A

Notes

A video illustrating the issue is attached to the bug report for your convenience