Fabric types
The first, and possibly most important, decision you have to make is what to spend your hard earned cash on. Everything else can be corrected as you go along but if you buy the wrong stuff then you're stuck. Basically inner layers should be linen and outer should be wool. The layers against the body need to be washed frequently, those on the outside need to be tough and water resistant.
Your shift, petticoat, coif and kirtle linings should be made of linen. Kentwell allows these to be cotton instead but I would strongly recommend linen, at least for your shift. Linen is cooler, more comfortable, wears and looks better, and is more accurate. Its disadvantages are that it's more expensive and harder to get hold of than cotton.
Linen's other disadvantage is that it shrinks substantially on washing. Before using it it's important to wash it on hot then tumble-dry it to get rid of all the shrinkage before it's sewn. It'll come out of the tumble dryer very stiff but will soften up on wearing and, each time it's washed, will get softer.Ali of Hert's fabrics sells linen at five pounds a meter and, unlike his wool, it's generally pretty good stuff. Ikea sells linen for 3.50 and I'm told that the bleached linen, although it seems incredibly stiff and rough in the store, washes up really nicely and is ideal for shifts. They call it aina for reasons best known to themselves. It comes in half a dozen colours - the light blue and the natural are the only ones really suitable for Kentwell but the bleached should take dylon beautifully. I use the natural linen to interline bodices and it's done me well so far.
For the outer layers, the best bet is wool. Wool comes in lots of weaves and weights; you're looking for the sort of stuff you'd buy a winter coat in. If you can, it's definately best to use pure wool. It's warmer in the cool and cooler in the sun than synthetics and is much safer round open fires. Synthetics burn and melt, wool smoulders and goes out. Even if you're indoors, you're going to end up sitting 'round a campfire with a bottle of something warming at some point, and the last thing you want is to burn a hole in your kirtle.
Wool also shrinks substantially on washing. It also thickens up and becomes more fluffy. I never wash my kirtle - that's what my linens are for - and I figure trying to stuff that much fabric in the machine is a mistake. However, if you will want to wash your wools you will need to wash them prior to cutting out. I would strongly suggest washing a beer-mat sized sample first just to check you're happy with the change in texture.
Like linen, wool can be hard to get hold of. Ikea do a beautiful bright blue for nine pounds a meter. I've never been very impressed with Ali's stuff but, if you can find anything on his stall, he's a bargain at a mere five quid. If you're near by there's a stall in Norwich Market that has fantastic wools (typically for between 10-12 pounds) and the Colchester remnant shop is very good for both wool and linen. Petty Chapman/Dave Rushworth sell fabric to die for but the contact details I have for them are out of date.
Tudor colours
Tudor fabric, with the exception of blue, appears to have been largely dyed 'in the cloth'. That is, it was woven and then dyed. So speckled or patterned fabric, or that woven from threads of different shades, is unlikely to be correct. This is a bit of an oversimplification (checked fabric was found on the Mary Rose, for example) but sticking to plain stuff should stop you falling foul of costume check. As a general rule of thumb, the brighter or darker the colours, the more dye is needed to produce them, so the more expensive they tended to be.
Shifts and coifs should be white, off-white or unbleached linen. Linen bleaches whiter with use and washing so anything except blue-tinted glaringly white whites is okay.
Greys are always correct. Look at sheep for an idea of acceptable shades: anything from dove to dark grey is achievable from the fleece.
Blues were produced from woad, which seems to have been grown in great quantities in Suffolk. Darker colours involve redipping the wool - more dye so more expense. Anything from washed out blue (watchet) to a bright sky blue is realistic at a low social scale. Avoid royal blue or navy - just too expensive.
Red comes from madder, which was being imported in great quantities from the lowlands to Norwich (the theatre there is still called "The Maddermarket"). Madder gives anything from salmon and apricot through to orange, reddish browns and brick red. Scarlet is not okay, nor is burgandy or red with bluish/purple undertones. If it was achievable at all it would have involved cochineal - prohibitively expensive. On linen, madder gives pink.
Believe it or not, screaming neon yellow is perfectly achievable with period dyes. It comes from weld and it's well worth walking by the dyers just to see how bright it is. I'd avoid making a kirtle out of it, though - there's a beetle on the manor that loves the colour and, if you wear it, you risk being covered by little black dots. The whole range of mustards, curry yellows, yellow-browns and browns through to chocolate (dyed with walnut) are fine.
Summary
As a rule of thumb, avoid the following:
These aren't hard and fast rules. You'll certainly find bright colours and patterns in the sixteenth century. But, if you're not sure what's correct, these guidelines should reduce the potential for expensive mistakes.