Duplicate the image layer repeatedly until the transparency is gone, then merge the duplicate layers.
Note: this will alter the soft white edge unless you mask that area before duplicating the layers. I would duplicate the image layer once, remove the soft white edge from the duplicate, then duplicate again until the internal translucency becomes opaque.
This way, the colors remain true, you simply build up the slight transparency with each duplication. 60% transparent stacked onto 60% transparent equals an area 100% opaque.