drain pipe and guutering

Some blacks can fade in direct sunlight. Some others (like the Brett cast iron effect I have) seem to fare a little better.

I think the flat bottomed section carries a more water and the black finish will last the longest. Mine has gone to light grey after about twenty years full sun - you can see extrusion stress lines in it now.

Try and pick a popular series of fittings too! It is incredibly annoying to have some short lived obscure size variant that requires a trip to a distant plumbing specialist every time something fails.

Standard black plastic on longish runs can creep due to thermal cycling. The most recent stuff here, fitted by a builder (unknown source) is white inside.

If you're replacing all your gutters, have you considered seamless aluminium gutters? These don't leak at the joints, because there aren't any! The gutters are constructed on-site to whatever length is required

- using a machine which takes a roll of powder-coated aluminium strip and forms it into the appropriate cross section for a gutter - usually with a flat bottom and deepish sides, so as to have a greater capacity than a semi-circular plastic gutter.

It comes in various colours - including brown - and, being powder coated, does not fade. As you might expect, it costs more than plastic, but you only have to do it once. [The down pipes are usually plastic, so these *will* fade over time - but replacing them is much easier than replacing the whole gutter system.]

If you Google for "Seamless Aluminium Gutter", you'll probably find a few local firms offering to supply and install it.

As an ex girlfriend once advised a friend, 'Black and brown do not suit each other'. I agree.

Square, -flat bottomed, as has been said-, has a little more volume which, may be better equipped to carry off larger volumes of water. IMO, it also looks better than round. But, that also depends on the features of the building.

If it was simply a matter of leakage at the joints, it may be possible to buy the sealing rubbers else, fill the joints with a heavy grease?

If you do replace it yourself, be sure to allow for expansion by leaving a 6mm gap from the 'butting' edge which is circa 75mm inside the outer edge of any coupling piece.

...Ray.

I thought white would yellow?