Help Preview mode question

[cookiesaurus 0]

in attached photo: 

(previewing sliced model in "line type")

 

GOAL: taper to a fine edge

PROBLEM: the shell?/skin? [outermost layer] not fusing together to a single line at the top of the print. 

 

1. why is part of the model yellow (top/bottom), while the rest is red (shell)?

 

2. What settings should I be using to make sure I have a continuous, solid edge at the top?

 

 

additional issue:

I have tried to use "spiralize" but when previewing the layers, there are still many travels.