This button using the well documented VML solution renders great across Outlook but only in light mode. In dark mode, I lose control over the "fillcolor" and am getting this black-ish overlay that obscures the cream-ish color—which is the one I want. Solutions?
<table align="left" role="presentation" cellspacing="0" cellpadding="0" border="0" width="100%" style="margin: auto;">
<tr>
<td class="content" align="left" style="background-color: #EFE9D9; font-family: 'Inter', Arial, sans-serif; padding-top:40px; padding-bottom: 40px;">
<table align="left" role="presentation" cellspacing="0" cellpadding="0" border="0" width="100%" style="margin: auto;">
<tr>
<td class="content" align="left" style="background-color: #EFE9D9; font-family: 'Inter', Arial, sans-serif">
<!--[if mso]>
<v:roundrect xmlns:v="urn:schemas-microsoft-com:vml" xmlns:w="urn:schemas-microsoft-com:office:word"
href="cnn.com"
title="cnn"
style="height:68px;v-text-anchor:middle;width:340;margin-left:25px; margin-right:25px;"
arcsize="58.82352941176471%" stroke="f" fillcolor="#181818"><w:anchorlock/>
<center>
<![endif]-->
<a href="%%=v(@Button_URL)=%%" class="dark-button button-td-primary" title="%%=v(@Button_title)=%%" alias="%%=v(@Button_alias)=%%"
style="text-decoration:none;
color:#EFE9D9;
background-color:#181818;
border-radius:40px;
border-top:0px;
font-weight:600;
border-right:0px;
border-bottom:0px;
border-left:0px;
padding-top:15px;
padding-bottom:15px;
font-family:'Inter', Arial, sans-serif;
font-size:16px;
text-align:center;
mso-border-alt:none;
word-break:keep-all;
mso-shading: transparent">
<span style="padding-left:25px;
padding-right:25px;
font-size:16px;
display:inline-block;
letter-spacing:normal;
word-break: break-word;">
Click me to visit cnn
</span>
</a>
<!--[if mso]></center></v:roundrect><![endif]-->
</td>
</tr>
</table>
</td>
</tr>
</table>
You have the best that can be hoped for, unfortunately.
Officially, Outlook Windows has no support for dark mode at all. It applies a 'blind invert', meaning even dark colours become light - it flips everything when it tries to make your emails dark. (See https://www.litmus.com/blog/the-ultimate-guide-to-dark-mode-for-email-marketers for full details)
The only hack developed for it works for text colour, but thankfully at least your dark mode button still has great contrast. (See hack here: https://webdesign.tutsplus.com/how-to-fix-outlook-dark-mode-problems--cms-37718t)
If it absolutely must be white (keeping in mind how few have dark mode Outlook desktop, and that even Outlook desktop is now being actively replaced with the new Outlook that closely resembles Outlook.com), you could use an image - but you lose accessibility, and for Outlook desktop users, they would have to consciously click to download pictures to see it.
