Healthy roots will be very light in color, almost white. Not the root bark, but the actual woody interior. Also, at the tips of these roots, there sould have been light colored "feeder" roots present. These threadlike growths should be abundant in a thriving tree.

Rotten roots will darken in color and there may even be a sour odor.

+oM

If the roots in general look mushy, then probably it was too much water. If there are white/yellowish roots/new growth at the ends of larger roots, the roots were pretty healthy - not too likely, I admit. If the root-ends are all brown and soft, and if they pull apart easily, then they rotted.

The next lot of trees/shrubs you plant, water them according to their needs, not on a schedule. After the first week or so, when you have tapered off from daily to every 3-4 days, stick a finger in the soil next to the root area - under the mulch if you have mulched around the tree(s) - and see if it is dry down about to the second knuckle. You can use a pointed dowel for this, in which case it should be damp down about 2". If it's still moist, wait and test again in a day or two. If it is dry, then you need to water long and slow, so it gets to the bottom of the root ball - only you can decide how long that takes - but more than 10-15 min. usually.

I don't know what soil you have, not how hot or windy or rainy the weather has been - all these can affect how quickly the soil dries out and to what degree and thus how quickly you need to water again. If you think that the soil tends to be overly damp much of the time, then planting future trees so that the top couple of inches of the root ball are above the ground line - make up the difference with a "ramp" of dirt and mulch, so it looks like the tree is planted on a mound - will help with keeping the roots properly moist but not drowning them.

If you didn't mulch, do so, as widely as possible, no deeper than 4", and put no mulch next to the trunk. Mulch helps moderate moisture and temperature swings, limits weed/grass root competition, and keeps errant lawn mowers and weed-eaters away from the vulnerable trunks. It also improves the soil as it breaks down, so don't use landscape fabric or plastic under it. If there is grass growing where you want to put mulch, either spray it with Round-up or lay down flattened cardboard or 4-6 overlapping sheets of black-ink newspaper under the mulch to smother the grass.

There is a type of mite that will infest Leyland Cypress as well. My grandparents planted hundreds of them along their property line and now there are gaps everywhere.