RFR: 8287743: javax/swing/text/CSSBorder/6796710/bug6796710.java failed

[Prasanta Sadhukhan]

Test is failing in iMac CI systems owing to color difference of 1

`x 0 y 0 rgb1: fff0f0f0 rgb2: fff0eff0`

Added minor color tolerance check. CI testing is green

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Commit messages:
 - 8287743: javax/swing/text/CSSBorder/6796710/bug6796710.java failed

Changes: https://git.openjdk.java.net/jdk/pull/9011/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9011&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287743
  Stats: 38 lines in 1 file changed: 37 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9011.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9011/head:pull/9011

PR: https://git.openjdk.java.net/jdk/pull/9011