BibTeX does not have the right entry for preprints. This is a hack for producing the correct reference:
@booklet{EasyChair:646,
author = {Xiaoran Cai and Yoshihisa Kanematsu and Kunio Kondo and Koji Mikami},
title = {The Research On Virtual Reality Sickness With Advancing Color And Receding Color},
howpublished = {EasyChair Preprint 646},
year = {EasyChair, 2018}}