If you are talking about "matching" caps and tubes from different manufacturers, be careful with that. Physical dimensions of tank parts are not standardized, including the thickness of the tubes used and the diameters of the caps and tubes.
The Phiniac tanks come with default black delrin endcaps. A black phrostie tube with those caps might be the effect that you are looking for.
Valley View Vapes has anodized aluminum caps in colors, including black. Their outer diameter is listed as 1 inch (25mm).
http://www.valleyvapes.com/Aluminum-Caps-for-3ml-and-6ml-PolyPro-Tanks_p_90.html
The clear Phiniac tubes' (which are used to make phrosties) outer diameter are listed as 22.5mm, so they are too slim to use with those caps.
The colored Phiniac tubes are listed as 25mm (amber, green, and cobalt) and might fit the VVV caps, but the black tubes appear to use a different thickness of glass so it's not clear to me if they have the same inner diameter as the other colored tubes.
Phiniac tube dimensions:
http://phiniac.com/cmspage.php?page_id=33
However, the measurement most important to you would be the inner diameter of the tubes, as that is what will be making contact for a good secure fit with the end caps. Phiniac's customer service has a helpful and friendly reputation and giving them a call likely could give you enough information to make a safe and satisfactory decision.
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I was able to match a color sandblasted design Phiniac with the endcaps of a Hoosier Vapes Elegance tank. This is a nice tank combo; the mouthpiece and top cap are one piece, and twists off of the tube for easy juice filling.
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