I spotted this bug in my garden last week.
It was about 8 to 10mm long and had an orange/red underside. The photo also doesn't really show up the red "shoulders" it has. Since first spotting it I've noticed that it appears to be subtly changing colour: the underside gettting paler in colour, the upperside and spots becoming more iridescent and green (rather than the almost black colour you see in the pic). Unfortunately I can't now take another picture of it because it's done a bunk!
Co-located on the same plant (a hollyhock since you were asking) were what I take to be the nymphs of the same bug.
Altogether I spotted about 14 nymphs over the plant, varying in size from about 2mm to 5mm.
From looking at the pictures elsewhere on this marvelous site I had assumed my bug to be some sort of shield bug - but what type? There doesn't appear to be any other matching pictures anywhere and it's driving me mad trying to identify this little blighter and its progeny.