Actually, with Tamiya those instruction DO mean to mix those paints...
X-11:1+X-26:1 means to mix X-11(chrome silver) and X-26 (clear orange) in a 1 to 1 ratio. That's what the :1 parts mean.
The reason it worked this time is becasue the clear oreange is clear... so the sliver shows thru. But if you did this coating with two opaque colors, you would only get the second color.
The X-6:1 + X-15:10 mean ONE part X-6 (orange) and TEN parts X-15 (light green). Did you mean XF-15 -- flat flesh, or X-15 -- light green??
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