You can use ZO_ColorDef class:
Lua Code:
local color = ZO_ColorDef:FromInterfaceColor(INTERFACE_COLOR_TYPE_ITEM_QUALITY_COLORS, _tData.quality)
d(color:Colorize("whatever"))
-- or
d("|c" .. color:ToHex() .. "whatever|r")
or write the conversion out yourself:
Lua Code:
local r, g, b = GetInterfaceColor(INTERFACE_COLOR_TYPE_ITEM_QUALITY_COLORS, _tData.quality)
d(("|c%02x%02x%02x%s|r"):format(r*255, g*255, b*255, "whatever"))