It's straightforward: Neg Art (in camera), light or no crop (I don't remember), no excessive sharpening (I swear! ;-).
The final effect is, IMO, a result of what was there at the time (I isolated this cloud, because it struck me as unusual) and the NEG mode. The image marked the beginning of a series of cloud/sky shots taken on the same day and in the same manner.
As anyone can see from my portfolio, I have little interest or affection for what we call 'digital art' or extensive processing that alters the natural image. On the other hand, there are some subjects which, at times, strike me as 'dramatic' when viewed with the naked eye but less so when banned by the camera. It is then that I've been known to 'fumble' a little with whatever I can think of to get something that can at least match my interest.
I realize that the colours and hues in this shot are less natural than they appear 'artificial' due to the chosen mode, but I accept this (here), since it is so obviously a negative. When this is not or less the case, I'd prefer to convert to grayscale.
I can't wait to get home and look at it on a decent monitor (this laptop just ain't cuttin' it). This is just abstract enough to make it look *almost* surreal. I love it. the General is correct about his sharpness observation, but I don't think that it's a negative, given the surrealism that I get from it. I think i would like to see some slightly richer hues as well, just because the negative sky looks a little peachy to me (I'd prefer the Vanilla Sky, but then I'd have to digress much further :))
Beautiful image. please post the method to the madness.
I like playing around with the colors in sky shots, but this looks pretty close to a straight inversion, which is not usually the best color combo in my opinion. I might be a teensy bit oversharp too, but I often like things with less sharpening than other folks.
The combination of cloud types, with the cumulus right down by the water makes a strong abstract of three major shapes, with a dynamic aspect accentuated by the streaky clouds.
I think it's an interesting "digital negative" (in the figurative sense) I personally would play around with more, but could be exactly what you want too.