Fiber connection question to Cisco 3560 switch

we are connecting a Cisco WS-C3750X-48T-L switch to a Cisco WS-C3560V2-24TS-S with Fiber. We have two SFP connectors in each switch. On the Cisco 3750, both connections are green. On the 3560, one is amber and one is green. We are able to send traffic from one switch to another but we aren't sure why one is amber. We want to combine the connectors so that we can send 2GB over the link. When we unplug either fiber connection on the Cisco 3560, the other connection turns green. My first question is why is one connection amber and secondly how do we combine the connections so that we can utilize 2GB.

 we are connecting  small network environment with one layer 3 Catalyst 3750 and two Catalyst 3560s running VLANs across them. All switches are placed in the same network rack.

There is some debate about how best to connect them together:

a) with LC fibre cables and SFP fibre adapters.

b) with CAT5e cables and SFP Gigabit adapters.

c) with Cisco Interconnect cables (but unfortunately we already have a bucket load of SFP gbic adapters

1) Is there any benefit of using fibre to interconnect them over such a short distance? (they're located above/below each other in the same rack!). If so, what are the benefits?

My understanding is that fibre really only offers better latency which is important over longer distances, and the SFP ports are gigabit no matter if you use fibre or CAT5e the speed is the same - therefore I can see no point in interconnecting them with fibre - but then again, I am not a Cisco expert.

So you have 2 fibers between switches which effectively creates a loop.  So spanning-tree would then just one of the ports down to break the loop.

What you want to do is setup an etherchannel connection between the switches using both of those ports on each switch.  This creates a virtual interface called a port-channel that looks like one connection from spanning-tree's viewpoint.  Then it will send traffic down both links

The use of fibre optic against Cat5e began to become popular when used to span different floors and/or building.  Unlike Cat5e which has a limit of 100 metres, specific fibre optic cables can go from short range (multi-mode) to long range (single-mode). Now if budget permits, I would always choose uplinks or inter-connection to be fibre optic over copper (Cat5/Cat5e or Cat6).

If fibre optic isn't feasible then get Cat6 instead.