>> Do you want to preserve...
>> ...the in-gamut colours?
>> ...the relationship between colours?
>> ...colour saturation?
>>
>> Colour space conversion is a complicated subject.
>
> Well, at this stage I'd like to know how to do all three.

Well if you only want to preserve the in-gamut colours then obviously you 
only need to tinker with the out-of-gamut ones.  For these colours I would 
tempted to move the colour in the xy plane towards the white point until it 
became in-gamut.  Of course here you lose any "difference" perception 
between in-gamut and out-gamut colours with similar hues.

If you want to preserve the relationship, then it gets harder because 
colours in the Yxy or sRGB spaces are not spaced evenly for human perception 
of "difference".  If you want to do it properly, convert your Yxy data into 
CIELAB or similar, I'd then choose three new primaries (not the sRGB 
primaries) that allow all your colour points to be represented as positive 
combinations of the primaries.  Of course here no colours will be properly 
displayed, but the relationships should be preserved.

You could also do a combination of the above two, whereby if a colour is 
within say the central 50% of sRGB you map it exactly, but then further out 
the colours get compressed to fit in the sRGB space, but still maintaining 
some sort of difference.  I think I saw some display processor from Philips 
once that did this.

> However, I am running into additional problems. I am converting the 1929 
> Munsell data set (http://www.cis.rit.edu/mcsl/online/munsell.php), and 
> *not a single one* of the colors lies completely within the SRGB gamut.

Just by looking at the numbers, the first one is xy=0.3532,0.2957 with a 
brightness of 3.126 cd/m2, that surely is within the sRGB space?

> You can test this by using the color converter found here:
>
> http://www.brucelindbloom.com/index.html?ColorCalculator.html

The first one comes out as RGB=(2.0,1.5,2.0) (rounded), seems to be within 
sRGB to me!

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