My family did this too.  My mothers brother is married to my fathers 
sister. My aunt and uncle never had children but we often joke that 
thier kids would have looked just like my brother, sister and I! It 
took years for my maternal grandmother to get over this, my maternal 
line is fair skinned with blue eyes and my paternal line is dark 
skinned. I believe my grandmother picked up her attitudes about skin 
color in Mexico.  Her fist question with grandchildren was always 
about their skin  and eye color.. This is also the grandmother who's 
line is where I found my Mulato slave line... I honestly don't think 
she knew...

In Tamazula Jalisco, my maternal grandfather's sister Rosa married his 
mother in laws brother Maximiano years before he married my 
grandmother. I'd have to assume that's how he met my grandmother... My 
aunt had photos that say these were the children of Maximiano and Rosa 
but no thought to mention they were double related.  It seemed to be 
norm in Mexico for there to be 20 year spans between first and last 
child so the age differences bring suitors that are family or friends 
from more than one generation.  When I have no ages I try to put at 
least 20 or 25 years for aprox. birth date but then I find a record of 
a 42 year old widower marrying a 14 year old girl 3 months after his 
wife dies in childbirth with their 14th child.  They then go on to 
have another 11 children. Can you just imagine being a mother of 14 at 
age 14! That had to  be an arrainged marriage.
Linda in Everett