I was looking online and found a site that makes custom leather collars and cuffs. However, I was wondering if a white collar had any different meaning than the more traditional black one?

Color preference for collars is simply that; a preference.  

Now, "flagging" or "hanky code" is a completely different thing.  That's where colors and placement DO have meaning.

I found an article about different types of collars and their meaning, but nothing I've read mentions any significance of various colors.  One site said that the Dominate may put something like a blue dog tag on a collar to signify a different stage of the relationship with his/her Submissive.

I would be very surprised if there isn't some form of color system somewhere in the BDSM community.  If I had to come up with one, I would borrow from the wiccan color code as an inspiration.
Just working with the three colors of yellow, orange and red for initiates may make things interesting from the point of good obedience and reward type of scenario.  Maybe use the colors to signify a task achievement like Yellow for Golden Shower, Brown for the full toilet, and Red for the red wings.  Just some ideas.  
Here are a few of the colors meaning in the Wiccan world.  The link has the rest.

COLOR

ASSOCIATIONS AND SYMBOLS

YELLOW
 Signifies: Knowledge, learning, concentration, persuasion, charm, confidence, jealousy, joy, comfort.
 Planet: Mercury
 Day: Wednesday
 Astrological Sign: Gemini, Leo  

 ORANGE
 Signifies: Encouragement, adaptability, stimulation, attraction, plenty, kindness.
 Holiday: Candlemas
 Deities: Brigid
 Planets: Sun, Mars, Mercury
 Days: Sunday, Tuesday, Wednesday
 Astrological Sign: Leo, Sagittarius  

 RED
 Signifies: Strength, health, vigor, lust, danger.
 Holiday: Yule
 Planet: Mars
 Day: Tuesday
 Astrological Sign: Scorpio

But, there's no widely accepted standard as far as I know.  

Some info I've found regarding collar colors: http://www.bdsmtrainingacademy.com/choosing-a-collar/

was during a period when I was between marriages and was very involved in a group with members in Phillie Baltimore NJ Delaware Maryland.  In that group a male wearing a pink color could be used for "forced" bi play. There was an attempt to have brown signify usable in toilet play but I was never in a gathering where this was featured, red was to mean you could break skin and black that the sub was owned by someone of color, but these never were used like that so only the pink on a male sub ever really had meaning.

END OF MESSAGE

I personally keep my equipment tradtional black or red unless gifted something...but I think pink would be suitable for sissy boi...

Using white or black could be fun if doing a racial scene....

When I thought of the yellow collar if made me think of watersports....the guys use to wear different color bandanas to show what they were into

pink!