How can you tell if baby is a silver laced or birchen? Do you look for certain patterns in the feathers etc!
Yes, basically you look for certain patterns in the feathers.
Sometimes it is patterns on each single feather (example: Silver Laced chickens have a black edge on each feather, with silver/white in the middle of the feather. When feathers like that are all over the chicken, it looks like someone spread a piece of black lace over a silver chicken.)
Other times, it is an overall pattern (example: Birchen chickens have black in some places, silver/white in other places, and specific arrangements of those colors on the individual feathers on certain parts of the body.)
Chicks sometimes have different color patterns than what they will have as adults, but they tend to get called by the name that goes with their adult color.
With practice, you can get better at recognizing what appearance of chick will go with what adult color. A few are easy (buff adults come from buff chicks, red adults usually come from red chicks) and some are harder (black adults come from chicks colored like black-and-yellow penguins). Chicks that are striped like little chipmunks when they hatch can grow up into adults with several different patterns of brown & black, or even white & black.
Some chickens have colors that don't really have names. This is especially common with mixed-breed chickens. For purebred chickens, every official variety has a name for their color (because someone gave that color a name, when they are working on getting it to look right and breed true.)