Convert int to RGB or hex color
Eithers of these 3 should work:

SELECT color
    , HEX_1 = '#'
        + CONVERT(varchar(6),
            CAST(ABS(color) as varbinary(1))
            + CAST(ABS(color/256) as varbinary(1))
            + CAST(ABS(color/256/256) as varbinary(1))
        , 2)
    , HEX_2 = '#'+
        +CONVERT(varchar(2), CAST(ABS(color) as varbinary(1)), 2)
        +CONVERT(varchar(2), CAST(ABS(color/256) as varbinary(1)), 2)
        +CONVERT(varchar(2), CAST(ABS(color/256/256) as varbinary(1)), 2)
    , RGB = 'rgb('
        + CAST(ABS(color)%256 as varchar(3)) + ','
        + CAST(ABS(color/256)%256 as varchar(3)) + ','
        + CAST(ABS(color/256/256)%256 as varchar(3)) + ')'
FROM (
    values 
        (-65280)
        , (-65535)
        , (-460293)
        , (-13606962)
        , (-3678732)
) as colors(color)


Output: 

color       | HEX_1     | HEX_2     | RGB
-65280      | #00FF00   | #00FF00   | rgb(0,255,0)
-65535      | #FFFF00   | #FFFF00   | rgb(255,255,0)
-460293     | #050607   | #050607   | rgb(5,6,7)
-13606962   | #32A0CF   | #32A0CF   | rgb(50,160,207)
-3678732    | #0C2238   | #0C2238   | rgb(12,34,56)


The CONVERT with style 2 requires SQL Server 2008 or later.

The expression could be used in a computed column definition, or inline table-valued function.