Since upgrade last night to v56.0.3051.36 on my Win 8, 64 Bit PC I immediately spotted a problem on one of my regular sites, not yet seen on other sites. Been using the site ADVFN, uk.advfn.com for many years with many different browsers and versions.
Their BB site (password access) has plain black text on a white background, the text entry/edit box is normally a simple black frame on the white background, entered text is normal black on white same as rest of BB. Opera v56 now shows body of this edit box in a light blue colour, with a band of darker blue at bottom (or top). Entered text now comes up as black on a darker blue background, like selected text. Moving cursor away changes text to black on the light blue background, like deselected. Resuming entry brings back 'Text Selected' dark blue background to text. Text selection applied inside box results in inverted text, white text on blue background, outside edit box selection is normal black text with dark blue background. After posting, the message appears normally. This blue shading to text also now appears in other text entry boxes on the site.
Also inconsistent across site. Sometimes the edit box has darker blue band at top, sometimes at bottom. Sometimes even seen 'normal' plain white background, though entered text still appears 'Selected'.