They are lovely Phoenix, but I have trouble getting mine to look as lovely as that. Mine always look more messy and less 'droppy'. Here's one I did the other day:
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FYI
@John Harris - to achieve this I split the batter into four colours - red, orange, green and TD to the base colour. I poured a little of the white ( about a cm coverage along the bottom of the mold) then poured a couple of random thin lines up and down of the red (from a height, so it 'drops' in), then the green, then the orange, then the white until all the colours were exhausted. As usual my batter got fairly thick for the last few passes along the top, so i grabbed a teaspoon and kinda spoon swirled the top inch or so of the top layers ( in, scoop, twist then out). Most people wouldn't have to bother with that if their batter is more fluid.