Why does the C# ternary operator appear to change the type of returned values?

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C#

I have the following if() statement:

if( _hexColourString.Length >= 8 )
    _bytes[ 3 ] = byte.Parse( _hexColourString.Substring( start + 6, 2 ), NumberStyles.AllowHexSpecifier );
else
    _bytes[ 3 ] = 0x00;

If I try to express this using the ternary operator, I get an error saying I cannot implicitly convert an int to a byte. The following does NOT compile:

_bytes[ 3 ] = ( _hexColourString.Length >= 8 ) ? byte.Parse( _hexColourString.Substring( start + 6, 2 ), NumberStyles.AllowHexSpecifier ) : 0x00;

So I thought I'd check which half of the ternary assignment was giving the problem. I took out the conditional part of the statement and wrote the two assignments as separate statements, like this:

_bytes[ 3 ] = byte.Parse( _hexColourString.Substring( start + 6, 2 ), NumberStyles.AllowHexSpecifier );
_bytes[ 3 ] = 0x00;

Both of these compile. The ternary operator seems to be changing the implicit type of one of the assignments (the literal 0x00).

Why does the plain assignment _bytes[ 3 ] = 0x00; compile okay without a cast but requires one when the expression is part of a ternary operator?

What I have tried:

As a final sanity check, I wanted to see conclusively which side of the assignment was causing the problem. I suspected the literal hex byte and I appear to be correct. The following pointless statement compiles:

_bytes[ 3 ] = ( _hexColourString.Length >= 8 ) ? byte.Parse( _hexColourString.Substring( start + 6, 2 ), NumberStyles.AllowHexSpecifier ) :
                byte.Parse( _hexColourString.Substring( start + 6, 2 ), NumberStyles.AllowHexSpecifier );

But the following equally pointless statement does NOT compile:

_bytes[ 3 ] = ( _hexColourString.Length >= 8 ) ? 0x00 : 0x00;