Oceans have colors computed from light scattering, that depends on the water depth. Besides, would you really want water color from Blue Marble, where it's clearly stated that it's been done that way just to make the oceans more interesting to look at when the BM data are used as maps. Real color is plain, except for shallow seas.
OT uses physical phenomena rendering to make it parametric. One thing that would be compatible with OT way would be adding maps that define, for example, how much bio stuff is in the sea (amount of oxygen in upper parts and stuff like that) so it can be included in the computation.
The data are wavelet-compressed so the size should be much smaller than that.
Landsat data are available for free, but the amount of processing needed is huge. The main problem are the clouds and the need to stitch the satellite scans together in seamless way. There are providers that offer the processed data, like TruEarth, but the prices start from $39,950 for uncompressed global data. GeoSage has better prices, however these seem to contain many visual artifacts.
We already got data for global 30m forest coverage and water bodies. These also happen to contain the red band of satellite data (together with near-infrared that's used for vegetation density computation), and it may be possible to use it to refine the 500m MODIS color data with it.
No, I meant you do not have to modify the input data, I wouldn't even want an arbitrarily modified surface reflectance to be baked in. The modifications should be expressed in the form of some filter coefficients acting on the source surface reflectance data. A post-processing, because that's basically what you want: you want to alter the real reflectance data to suit your taste. I do not know which filter coefficients I'll be able to expose yet, but I guess it generally could be a 4x4 matrix that multiplies the input YUV/veg color vector, or in a simple form a bias and multiplier for each color component. No simple 'shoping 
I was seeing earth pics from the iss and its true, the sea in blue marble is exagerated.. So you are right in that. No sense at all to fake it.
No, my intention in this topic is not exactly buy a personalized way in how outerra look.
What i will try is take all the juice from your engine focusing in the little details around light and colors, always with real references as i do always in my job.
Trying be as objetive as posible.
I will touch step by step all kind of situations. Day, afternoon, night, and hope can be useful for you developing (or not, if you dont think so, its alright, but i think i will make u trust in my taste a bit..).
Its a "betatester" way of play ur engine and use my "deformation" profesional in it ).
Its for fun and for take those renders to the limits..
SO now some RAW image from outerra. (with some trick i will explain after)
note: with the old tool for lighting shadows i would get almost the same result of the reference pic.
