Delete this code here:

.plurk_cnt:not([class*="metro"]) {
background: transparent !important;
color: #d6d6d9;
}

Or, if you want that beige color, change it to this:

.plurk_cnt:not([class*="metro"]) {
background: #d6d6d9 !important;
}

I couldn't quite test the color on my own due to having different coding overriding it with !important commands, but so long as you take out the transparent !important part, your timeline plurks will stop being transparent.

basically, the new code push (from what I can tell) prioritizes !important over secondary characteristics like color when determining backgrounds. You should still have the transparent overlay effect in your coding on hover, since that line of code was overriding just how plurks show up and not hover effects. If it's still too transparent to see clearly, just remove the /*-- Plurk transparency --*/ section, even though your plurks won't do the fancy fade in and out thing.

Hope this helps!