Gold - A serum-separating tube (SST). These contain particles that cause blood to clot quickly, as well as a gel to separate blood cells from serum. (Because the blood has clotted before it has been centrifuged, the liquid part is called serum not plasma.) 

Orange - These tubes contain thrombin which makes the blood clot extremely rapidly. This allows the serum to be analysed in a shorter time. 

Containers containing anticoagulants

Green - Contains the lithium salt of heparin, an anticoagulant. Also may contain ammonium or sodium salts of heparin. 

Purple or lavender - contains EDTA (the potassium salt, or K2EDTA). This is a strong anticoagulant and these tubes are usually used for full blood counts and blood films. Can also be used for blood banks. 

Grey - These tubes contain fluoride and oxalate. Fluoride prevents enzymes in the blood from working, so a substrate such as glucose will not be gradually used up during storage. Oxalate is an anticoagulant. 

Light blue - Contain a measured amount of citrate. Citrate is a reversible anticoagulant, and these tubes are used for coagulation assays. Because the liquid citrate dilutes the blood, it is important the tube is full so the dilution is properly accounted for. 

Dark Blue - Contains the sodium salt of heparin, an anticoagulant. Also can contain EDTA as an additive or have no additive. These tubes are used for trace metal analysis. 

Pink - Similar to purple tubes (both contain EDTA) these are used for ABO grouping and cross-matching. 

Others

Red - Contains no additives. Tests for antibodies and drugs often require these. 

Light yellow - Used in HLA phenotyping. Also contains SPS, used for blood cultures. 

Speckled top - no anticoagulant. Also called a "tiger top" tube. Contains clot activator more reading by http://freehdsex.net/en/