I'd suggest having your vet check for a possible urinary tract infection.
That is the most likely reason for colored material in the urine you are seeing.
If she is far enough along that she has a sticky vulva, with the stickiness picking up some dirt, the urine may be washing the vulva a bit clean as it passes resulting in dark streaks. If you wash off the vulva area and she still has dark material in the urine then a vet check up is the best option.
Make sure you let the vet know she is pregnant so the medications suggested will be safe for a pregnant dog to use.
Hope this helps you!
If you can take her temperature you might check that.
Here's my general 'check up' to decide if the emergency vet is needed -
If your dog might have gotten into anything toxic (including toxic plants), appears dehydrated (see if a pinch of skin over the shoulder blade stays stuck in a tent form or flows back down normally when released), has a rectal temp over 103.5F (normal is 100.5-102.5 Fahrenheit or 38 - 39.2 Celsius ), has gums or tongue that look white, blue, gray or yellow tinted where they are normally pink, has a slow color refill if you press on a pink area of gum or tongue, is having difficulty breathing, or is becoming more lethargic and non responsive to you as time goes on then you may want to get the dog in to see an emergency vet if one is available in your area.
This site may help you locate an emergency vet if you need one
http://www.vetlocator.com/hotline.php
Otherwise you may want to see your vet first thing when they open.
To cool dogs down you can dampen down their coats and set up a fan to blow a breeze on them. The evaporation from their damp coats should make them more comfortable.
You didn't say how far along she is but if she is spotting blood or dark color when not urinating (ie staining bedding) you might want to see a vet about that too as it could indicate uterine infection or loss of a fetus.
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30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics