I don't have a high-quality camera capable of capturing such details, but I have a professional calibrated S-IPS screen (which goes way above the standard NTSC color gamut, 128% to be precise) which dwarfs any MVA/PVA and TN-Film LCD panel out there, and of course it will look way better than on the N900. But it is foolish to compare such a screen to the N900's... You seem to have some heavy misconceptions about the display technology.

1) There is no such a thing as 32-bit color depth when it comes to screens. For a real 32-bit color palette (that is 8 bits per color + 8 bits for the alpha channel) you'd need to have a screen that is capable of achieving alpha on its pixels, and so far not even commercially available transparent OLED screens cannot do that. 32-bit was chosen for the exact same reason as 16-bit is used on the N900 even tho it is able to handle 18-bit - ease of programming. 32-bit is a size of an unsigned integer in almost every programming language, and 16-bit is unsigned short (and 8-bit is a byte), so you can easily manipulate pixels as numbers, in a computer and memory friendly way without non-standard bitwising overhead. Of those 32-bit that Windows reports, only the lower 24 bits are used (R(8b) + G(8b) + B(8b)) - alpha channel is completely ignored.

2) N900 has a TN-Film LCD, just like all the other smartphones out there with an LCD screen (and 99.5% laptops as well), and TN-Film cannot show a 24-bit palette - it uses 6 bits per color, hence it cannot physically show more than 64 levels per color, and thus the maximum color depth it can show is 18-bit, or 262144 colors (R(6b) + G(6b) + B(6b)). You can set the frame buffer to 64 bit if you like, but the screen will show only 18-bit. You cannot physically have more colors than that on N900. And you cannot have more colors than that on cheapo desktop monitors as well!

3) 6-bit is a non-standard data size and it would be extremely difficult and impractical to use it. As I've said, no sane programmer would want to change every single graphic library to accommodate such non-standard behavior. There are three possible approaches to using such a display:

1. To use a 24-bit frame buffer, where the screen's controller would try to interpolate the unavailable colors by dithering methods
2. To use a 18-bit frame buffer where you'd have a huge processing and programming overhead working with non-standard data types
3. To use the first lower-depth frame buffer of standard size, which in this case is 16-bit (R(5b) + G(5b) + B(5b), the highest bit is ignored), where you have no overheads.

While the first solution could potentially result in a better color reproduction (you have physical access to four times more colors than when limited to 16 bit), and which is precisely why it is used on desktop computers, you need to put the things in the right context - a mobile device does not have necessarily enough power and/or memory to handle such overhead gracefully, and the more data needed to be processed eats more battery. Further, you don't have a luxury of a high-powered graphic card (graphic cards in computers of today, even the cheapest ones, usually feature a high-powered RAMDAC working on 400+MHz - by itself its almost as powerful as the CPU of N900) and huge amount of memory so you can waste a full byte per pixel (on N900's screen that would be 384kb overhead, and trust me, that is a lot for a mobile device), and displays themselves have powerful controllers for dithering that eat more juice - and all that while you don't have to worry about extreme miniaturization and without concerns for battery usage.

The second approach is so silly that, to repeat, no sane programmer would consider it.

So, the third option is the most practical for a device such as N900. Yes, you get a lesser number of colors, but you massively gain on the performance and battery life, which is in this use case much more important than being able to show a full-available color fidelity on such a tiny screen. Nobody will do serious graphic work on the N900, actually nobody would do it on a TN-Film screen even if dithered, so I don't see what's the problem there. Sure, N900 could theoretically do it, but Hildon would probably need to be rewritten, there would be a serious performance impact, and I'm not clear whether there is a ditherer within the screen controller in the N900 at all, so that would probably need to be written as well further adding on the performance impact; I won't even comment how would that affect the battery life.

You couldn't be more wrong. Color fidelity is but a note in a long list of requirements for a quality screen. Quality screen does not need to be color at all, there are far more important properties to be considered first - a quality screen may not do all the things possible, but what little it does, it does on a professional level in an appliance that needs those properties. For a CAD designer screen geometry, sharpness and precision are of utter importance, for a print designer correct color reproduction is imperative, for trade shows the most important aspect is angle of viewing etc. TN-Film screens try to do a bit of everything, and they excel at nothing except the price and power consumption - which is actually a quality in the context of mobile devices where aforementioned qualities are not as much important.

So, with everything said, N900 has an exceptional screen for such a device. And there is quite a small number of mobile devices with a screen on par with N900's - and none of those has higher color palette (except those featuring OLED screens, but then you get other issues such as inability to see anything on them in a brightly lit room or under a direct sunlight, seriously crippling them as mobile devices).